SlideShare une entreprise Scribd logo
1  sur  809
Télécharger pour lire hors ligne
4O LESSONS ON REFRIGERATION AND AIR CONDITIONING FROM IIT
   KHARAGPUR. USEFUL TRAINING MATERIAL FOR MECHANICAL
ENGINEERING STUDENTS/COLLEGE, OR AS REFERENCE FOR ENGINEER.




                 EE IIT, Kharagpur, India

                          2008
Contents:

Lesson                                                                                     Page

Lesson 1 History Of Refrigeration [Natural Refrigeration ~ Artificial                        7
Refrigeration ]


Lesson 2 History Of Refrigeration - Development Of Refrigerants And                         26
Compressors [ Refrigerant development - a brief history ~ Compressor
development - a brief history ]


Lesson 3 Applications Of Refrigeration & Air Conditioning [ Application of                  44
refrigeration in Food processing, preservation and distribution ~ Applications of
refrigeration in chemical and process industries ~ Special applications of refrigeration
~ Application of air conditioning ]


Lesson 4 Review of fundamental principles - Thermodynamics : Part I [                       64
Definitions ~ Thermodynamic properties ~ Fundamental laws of Thermodynamics ]


Lesson 5 Review of fundamental principles - Thermodynamics : Part II [                      78
Thermodynamic relations ~ Evaluation of thermodynamic properties ~
Thermodynamic processes ]


Lesson 6 Review of fundamentals: Fluid flow [ Fluid flow ]                                  93
Lesson 7 Review of fundamentals: Heat and Mass transfer [ Heat transfer ~                  104
Fundamentals of Mass transfer ~ Analogy between heat, mass and momentum
transfer ~ Multimode heat transfer ~ Heat exchangers ]


Lesson 8 Methods of producing Low Temperatures [ Sensible cooling by cold                  124
medium ~ Endothermic mixing of substances ~ Phase change processes ~ Expansion
of Liquids ~ Expansion of gases ~ Thermoelectric Refrigeration ~ Adiabatic
demagnetization ]


Lesson 9 Air cycle refrigeration systems [ Air Standard Cycle analysis ~ Basic             138
concepts ~ Reversed Carnot cycle employing a gas ~ Ideal reverse Brayton cycle ~
Aircraft cooling systems ]
Lesson 10 Vapour Compression Refrigeration Systems [ Comparison                        153
between gas cycles and vapor cycles ~ Vapour Compression Refrigeration Systems ~
The Carnot refrigeration cycle ~ Standard Vapour Compression Refrigeration System
(VCRS) ~ Analysis of standard vapour compression refrigeration system ]


Lesson 11 Vapour Compression Refrigeration Systems: Performance                        171
Aspects And Cycle Modifications [ Performance of SSS cycle ~ Modifications to
SSS cycle ~ Effect of superheat on system COP ~ Actual VCRS systems ~ Complete
vapour compression refrigeration systems ]


Lesson 12 Multi-Stage Vapour Compression Refrigeration Systems [ Flash                 193
gas removal using flash tank ~ Intercooling in multi-stage compression ~ Multi-stage
system with flash gas removal and intercooling ~ Use of flash tank for flash gas
removal ~ Use of flash tank for intercooling only ]


Lesson 13 Multi-Evaporator And Cascade Systems [ Individual evaporators                213
and a single compressor with a pressure-reducing valve ~ Multi-evaporator system
with multi-compression, intercooling and flash gas removal ~ Multi-evaporator
system with individual compressors and multiple expansion valves ~ Limitations of
multi-stage systems ~ Cascade Systems ]


Lesson 14 Vapour Absorption Refrigeration Systems [ Maximum COP of ideal               238
absorption refrigeration system ~ Properties of refrigerant-absorbent mixtures ~
Basic Vapour Absorption Refrigeration System ~ Refrigerant-absorbent combinations
for VARS ]


Lesson 15 Vapour Absorption Refrigeration Systems Based On Water-                      258
Lithium Bromide Pair [ Properties of water-lithium bromide solutions ~ Steady
flow analysis of Water-Lithium Bromide Systems ~ Practical problems in water-
lithium bromide systems ~ Commercial systems ~ Heat sources for water-lithium
bromide systems ~ Minimum heat source temperatures for LiBr-Water systems ~
Capacity control ]


Lesson 16 Vapour Absorption Refrigeration Systems Based On Ammonia-                    279
Water Pair [ Properties of ammonia-water solutions ~ Basic Steady-Flow Processes
with binary mixtures ]


Lesson 17 Vapour Absorption Refrigeration Systems Based On Ammonia-                    301
Water Pair [ Working principle ~ Principle of rectification column and dephlegmator
~ Steady-flow analysis of the system ~ Pumpless vapour absorption refrigeration
systems ~ Solar energy driven sorption systems ~ Comparison between compression
and absorption refrigeration systems ]
Lesson 18 Refrigeration System Components: Compressors [ Compressors ~                 317
Reciprocating compressors ]


Lesson 19 Performance Of Reciprocating Compressors [ Ideal compressor                  337
with clearance ~ Actual compression process ~ Capacity control of reciprocating
compressors ~ Compressor lubrication ]


Lesson 20 Rotary, Positive Displacement Type Compressors [ Rolling piston              361
(fixed vane) type compressors ~ Multiple vane type compressors ~ Characteristics of
rotary, vane type compressors ~ Rotary, screw compressors ~ Scroll compressors ]


Lesson 21 Centrifugal Compressors [ Analysis of centrifugal compressors ~              376
Selection of impeller Speed and impeller diameter ~ Refrigerant capacity of
centrifugal compressors ~ Performance aspects of centrifugal compressor ~
Commercial refrigeration systems with centrifugal compressors ]


Lesson 22 Condensers & Evaporators [ Condensers ~ Classification of                    402
condensers ~ Analysis of condensers ~ Optimum condenser pressure for lowest
running cost ]


Lesson 23 Condensers & Evaporators [ Classification ~ Natural Convection type          439
evaporator coils ~ Flooded Evaporator ~ Shell-and-Tube Liquid Chillers ~ Shell-and-
Coil type evaporator ~ Double pipe type evaporator ~ Baudelot type evaporators ~
Direct expansion fin-and-tube type ~ Plate Surface Evaporators ~ Plate type
evaporators ~ Thermal design of evaporators ~ Enhancement of heat transfer
coefficients ~ Wilson's plot ]


Lesson 24 Expansion Devices [ Capillary Tube ~ Automatic Expansion Valve (AEV)         465
~ Flow Rate through orifice ~ Thermostatic Expansion Valve (TEV) ~ Float type
expansion valves ~ Electronic Type Expansion Valve ~ Practical problems in operation
of Expansion valves ]


Lesson 25 Analysis Of Complete Vapour Compression Refrigeration                        504
Systems [ Reciprocating compressor performance characteristics ~ Evaporator
Performance ~ Expansion valve Characteristics ~ Condensing unit ~ Performance of
complete system - condensing unit and evaporator ~ Effect of expansion valve ]


Lesson 26 Refrigerants [ Primary and secondary refrigerants ~ Refrigerant              523
selection criteria ~ Designation of refrigerants ~ Comparison between different
refrigerants ]
Lesson 27 Psychrometry [ Methods for estimating properties of moist air ~                 537
Measurement of psychrometric properties ~ Calculation of psychrometric properties
from p, DBT and WBT ~ Psychrometer ]


Lesson 28 Psychrometric Processes [ Important psychrometric processes ~ Air               553
Washers ~ Enthalpy potential ]


Lesson 29 Inside And Outside Design Conditions [ Selection of inside design               572
conditions ~ Thermal comfort ~ Heat balance equation for a human being ~ Factors
affecting thermal comfort ~ Indices for thermal comfort ~ Predicted Mean Vote
(PMV) and Percent People Dissatisfied (PPD) ~ Selection of outside design conditions
]


Lesson 30 Psychrometry Of Air Conditioning Systems [ Summer air                           591
conditioning systems ~ Guidelines for selection of supply state and cooling coil ]


Lesson 31 Evaporative, Winter And All Year Air Conditioning Systems [                     608
Introduction to evaporative air conditioning systems ~ Classification of evaporative
cooling systems ~ Advantages and disadvantages of evaporative cooling systems ~
Applicability of evaporative cooling systems ~ Winter Air Conditioning Systems ~ All
year (complete) air conditioning systems ~ ]


Lesson 32 Cooling And Heating Load Calculations - Estimation Of Solar                     626
Radiation [ Solar radiation ~ Calculation of direct, diffuse and reflected radiations ]

Lesson 33 Cooling And Heating Load Calculations -Solar Radiation                          645
Through Fenestration - Ventilation And Infiltration [ Solar radiation through
fenestration ~ Estimation of solar radiation through fenestration ~ Effect of external
shading ~ Ventilation for Indoor Air Quality (IAQ) ~ Infiltration ~ Heating and cooling
loads due to ventilation and infiltration ]


Lesson 34 Cooling And Heating Load Calculations - Heat Transfer Through                   660
Buildings - Fabric Heat Gain/Loss [ One-dimensional, steady state heat transfer
through buildings ~ Unsteady heat transfer through opaque walls and roofs ~ One-
dimensional, unsteady heat transfer through building walls and roof ]


Lesson 35 Cooling And Heating Load Calculations - Estimation Of                           688
Required Cooling/Heating Capacity [ Heating versus cooling load calculations ~
Methods of estimating cooling and heating loads ~ Cooling load calculations ~
Estimation of the cooling capacity of the system ~ Heating load calculations ~ ]
Lesson 36 Selection Of Air Conditioning Systems [ Selection criteria for air                 709
conditioning systems ~ Classification of air conditioning systems ~ All water systems ~
Air-water systems ~ Unitary refrigerant based systems ]


Lesson 37 Transmission Of Air In Air Conditioning Ducts [ Transmission of air                734
~ Flow of air through ducts ~ Estimation of pressure loss in ducts ~ Dynamic losses in
ducts ~ Static Regain ]


Lesson 38 Design Of Air Conditioning Ducts [ General rules for duct design ~                 752
Classification of duct systems ~ Commonly used duct design methods ~ Performance
of duct systems ~ System balancing and optimization ~ Fans ]


Lesson 39 Space Air Distribution [ Design of air distribution systems ~ Behaviour            772
of free-stream jet ~ Circular jets ~ Types of air distribution devices ~ Return air inlets
~ Airflow patterns inside conditioned space ~ Stratified mixing flow ~ Spot
cooling/heating ~ Selection of supply air outlets ]


Lesson 40 Ventilation For Cooling [ Natural versus mechanical ventilation ~                  797
Natural ventilation ~ Guidelines for natural ventilation ~ Forced ventilation using
electric fans ~ Interior air movement ]


Reference books for this course                                                              809
Lesson
                                      1
History Of Refrigeration

          1    Version 1 ME, IIT Kharagpur
Objectives of the lesson:
The objectives of this lesson are to:

   1. Define refrigeration and air conditioning (Section 1.1)

   2. Introduce aspects of various natural refrigeration methods, namely:

           a.   Use of ice transported from colder regions (Section 1.2)
           b.   Use of ice harvested in winter and stored in ice houses (Section 1.2)
           c.   Use of ice produced by nocturnal cooling (Section 1.2.1)
           d.   Use of evaporative cooling (Section 1.2.2)
           e.   Cooling by salt solutions (Section 1.2.3)

   3. Introduce historical aspects of various artificial refrigeration methods, namely:

           a. Vapour compression refrigeration systems, including
                  i. Domestic refrigeration systems (Section 1.3.1.1)
                 ii. Air conditioning systems (Section 1.3.1.2)
           b. Vapour absorption refrigeration systems (Section 1.3.2)
           c. Solar energy based refrigeration systems (Section 1.3.3)
           d. Air cycle refrigeration systems (Section 1.3.4)
           e. Steam and vapor jet refrigeration systems (Section 1.3.5)
           f. Thermoelectric refrigeration systems (Section 1.3.6), and
           g. Vortex tubes (Section 1.3.7)

At the end of the lesson the student should be able to:

   1. Identify various natural and artificial methods of refrigeration

   2. List salient points of various refrigeration techniques, and

   3. Name important landmarks in the history of refrigeration

1.1. Introduction
        Refrigeration may be defined as the process of achieving and maintaining a
temperature below that of the surroundings, the aim being to cool some product or space to
the required temperature. One of the most important applications of refrigeration has been the
preservation of perishable food products by storing them at low temperatures. Refrigeration
systems are also used extensively for providing thermal comfort to human beings by means
of air conditioning. Air Conditioning refers to the treatment of air so as to simultaneously
control its temperature, moisture content, cleanliness, odour and circulation, as required by
occupants, a process, or products in the space. The subject of refrigeration and air
conditioning has evolved out of human need for food and comfort, and its history dates back
to centuries. The history of refrigeration is very interesting since every aspect of it, the
availability of refrigerants, the prime movers and the developments in compressors and the
methods of refrigeration all are a part of it. The French scientist Roger ThÝvenot has written
an excellent book on the history of refrigeration throughout the world. Here we present only a



                                               2                Version 1 ME, IIT Kharagpur
brief history of the subject with special mention of the pioneers in the field and some
important events.

Q: Which of the following can be called as a refrigeration process?

a) Cooling of hot ingot from 1000oC to room temperature
b) Cooling of a pot of water by mixing it with a large block of ice
c) Cooling of human beings using a ceiling fan
d) Cooling of a hot cup of coffee by leaving it on a table
e) Cooling of hot water by mixing it with tap water
f) Cooling of water by creating vacuum over it

Ans: b) and f)

1.2. Natural Refrigeration
       In olden days refrigeration was achieved by natural means such as the use of ice or
evaporative cooling. In earlier times, ice was either:

   1. Transported from colder regions,
   2. Harvested in winter and stored in ice houses for summer use or,
   3. Made during night by cooling of water by radiation to stratosphere.

        In Europe, America and Iran a number of icehouses were built to store ice. Materials
like sawdust or wood shavings were used as insulating materials in these icehouses. Later on,
cork was used as insulating material. Literature reveals that ice has always been available to
aristocracy who could afford it. In India, the Mogul emperors were very fond of ice during
the harsh summer in Delhi and Agra, and it appears that the ice used to be made by nocturnal
cooling.

         In 1806, Frederic Tudor, (who was later called as the “ice king”) began the trade in
ice by cutting it from the Hudson River and ponds of Massachusetts and exporting it to
various countries including India. In India Tudor’s ice was cheaper than the locally
manufactured ice by nocturnal cooling. The ice trade in North America was a flourishing
business. Ice was transported to southern states of America in train compartments insulated
by 0.3m of cork insulation. Trading in ice was also popular in several other countries such as
Great Britain, Russia, Canada, Norway and France. In these countries ice was either
transported from colder regions or was harvested in winter and stored in icehouses for use in
summer. The ice trade reached its peak in 1872 when America alone exported 225000 tonnes
of ice to various countries as far as China and Australia. However, with the advent of
artificial refrigeration the ice trade gradually declined.

1.2.1. Art of Ice making by Nocturnal Cooling:

        The art of making ice by nocturnal cooling was perfected in India. In this method ice
was made by keeping a thin layer of water in a shallow earthen tray, and then exposing the
tray to the night sky. Compacted hay of about 0.3 m thickness was used as insulation. The
water looses heat by radiation to the stratosphere, which is at around -55˚C and by early
morning hours the water in the trays freezes to ice. This method of ice production was very
popular in India.



                                               3               Version 1 ME, IIT Kharagpur
1.2.2. Evaporative Cooling:

        As the name indicates, evaporative cooling is the process of reducing the temperature
of a system by evaporation of water. Human beings perspire and dissipate their metabolic
heat by evaporative cooling if the ambient temperature is more than skin temperature.
Animals such as the hippopotamus and buffalo coat themselves with mud for evaporative
cooling. Evaporative cooling has been used in India for centuries to obtain cold water in
summer by storing the water in earthen pots. The water permeates through the pores of
earthen vessel to its outer surface where it evaporates to the surrounding, absorbing its latent
heat in part from the vessel, which cools the water. It is said that Patliputra University
situated on the bank of river Ganges used to induce the evaporative-cooled air from the river.
Suitably located chimneys in the rooms augmented the upward flow of warm air, which was
replaced by cool air. Evaporative cooling by placing wet straw mats on the windows is also
very common in India. The straw mat made from “khus” adds its inherent perfume also to the
air. Now-a-days desert coolers are being used in hot and dry areas to provide cooling in
summer.

1.2.3. Cooling by Salt Solutions:

        Certain substances such as common salt, when added to water dissolve in water and
absorb its heat of solution from water (endothermic process). This reduces the temperature of
the solution (water+salt). Sodium Chloride salt (NaCl) can yield temperatures up to -20˚C
and Calcium Chloride (CaCl2) up to - 50˚C in properly insulated containers. However, as it is
this process has limited application, as the dissolved salt has to be recovered from its solution
by heating.

Q. The disadvantages of natural refrigeration methods are:

a) They are expensive
b) They are uncertain
c) They are not environment friendly
d) They are dependent on local conditions

Ans: b) and d)

Q. Evaporative cooling systems are ideal for:

a) Hot and dry conditions
b) Hot and humid conditions
c) Cold and humid conditions
d) Moderately hot but humid conditions

Ans: a)




                                                4               Version 1 ME, IIT Kharagpur
1.3. Artificial Refrigeration
        Refrigeration as it is known these days is produced by artificial means. Though it is
very difficult to make a clear demarcation between natural and artificial refrigeration, it is
generally agreed that the history of artificial refrigeration began in the year 1755, when the
Scottish professor William Cullen made the first refrigerating machine, which could produce
a small quantity of ice in the laboratory. Based on the working principle, refrigeration
systems can be classified as vapour compression systems, vapour absorption systems, gas
cycle systems etc.

1.3.1. Vapour Compression Refrigeration Systems:

        The basis of modern refrigeration is the ability of liquids to absorb enormous
quantities of heat as they boil and evaporate. Professor William Cullen of the University of
Edinburgh demonstrated this in 1755 by placing some water in thermal contact with ether
under a receiver of a vacuum pump. The evaporation rate of ether increased due to the
vacuum pump and water could be frozen. This process involves two thermodynamic
concepts, the vapour pressure and the latent heat. A liquid is in thermal equilibrium with its
own vapor at a pressure called the saturation pressure, which depends on the temperature
alone. If the pressure is increased for example in a pressure cooker, the water boils at higher
temperature. The second concept is that the evaporation of liquid requires latent heat during
evaporation. If latent heat is extracted from the liquid, the liquid gets cooled. The temperature
of ether will remain constant as long as the vacuum pump maintains a pressure equal to
saturation pressure at the desired temperature. This requires the removal of all the vapors
formed due to vaporization. If a lower temperature is desired, then a lower saturation pressure
will have to be maintained by the vacuum pump. The component of the modern day
refrigeration system where cooling is produced by this method is called evaporator.

    If this process of cooling is to be made continuous the vapors have to be recycled by
condensation to the liquid state. The condensation process requires heat rejection to the
surroundings. It can be condensed at atmospheric temperature by increasing its pressure. The
process of condensation was learned in the second half of eighteenth century. U.F. Clouet and
G. Monge liquefied SO2 in 1780 while van Marum and Van Troostwijk liquefied NH3 in
1787. Hence, a compressor is required to maintain a high pressure so that the evaporating
vapours can condense at a temperature greater than that of the surroundings.

    Oliver Evans in his book “Abortion of a young Steam Engineer’s Guide” published in
Philadelphia in 1805 described a closed refrigeration cycle to produce ice by ether under
vacuum. Jacob Perkins, an American living in London actually designed such a system
in1835. The apparatus described by Jacob Perkins in his patent specifications of 1834 is
shown in Fig.1.1. In his patent he stated “I am enabled to use volatile fluids for the purpose of
producing the cooling or freezing of fluids, and yet at the same time constantly condensing
such volatile fluids, and bringing them again into operation without waste”.




                                               5                Version 1 ME, IIT Kharagpur
Fig. 1.1. Apparatus described by Jacob Perkins in his patent specification of 1834.
       The refrigerant (ether or other volatile fluid) boils in evaporator B taking heat from
       surrounding water in container A. The pump C draws vapour away and compresses it
       to higher pressure at which it can condense to liquids in tubes D, giving out heat to
       water in vessel E. Condensed liquid flows through the weight loaded valve H, which
       maintains the difference of pressure between the condenser and evaporator. The small
       pump above H is used for charging the apparatus with refrigerant.

       John Hague made Perkins’s design into working model with some modifications. This
Perkins machine is shown in Fig.1.2. The earliest vapour compression system used either
sulphuric (ethyl) or methyl ether. The American engineer Alexander Twining (1801-1884)
received a British patent in 1850 for a vapour compression system by use of ether, NH3 and
CO2.

       The man responsible for making a practical vapor compression refrigeration system
was James Harrison who took a patent in 1856 for a vapour compression system using ether,
alcohol or ammonia. Charles Tellier of France patented in 1864, a refrigeration system using
dimethyl ether which has a normal boiling point of −23.6˚C.




                                             6               Version 1 ME, IIT Kharagpur
Fig.1.2. Perkins machine built by John Hague

        Carl von Linde in Munich introduced double acting ammonia compressor. It required
pressures of more than 10 atmospheres in the condenser. Since the normal boiling point of
ammonia is -33.3˚C, vacuum was not required on the low pressure side. Since then ammonia
is used widely in large refrigeration plants.

        David Boyle, in fact made the first NH3 system in 1871 in San Francisco. John
Enright had also developed a similar system in 1876 in Buffalo N.Y. Franz Windhausen
developed carbon dioxide (CO2) based vapor compression system in Germany in 1886. The
carbon dioxide compressor requires a pressure of about 80 atmospheres and therefore a very
heavy construction. Linde in 1882 and T.S.C. Lowe in 1887 tried similar systems in USA.
The CO2 system is a very safe system and was used in ship refrigeration until 1960s. Raoul
Pictet used SO2 (NBP -10˚C) as refrigerant. Its lowest pressure was high enough to prevent
the leakage of air into the system.

       Palmer used C2H5Cl in 1890 in a rotary compressor. He mixed it with C2H5Br to
reduce its flammability. Edmund Copeland and Harry Edwards used iso-butane in 1920 in
small refrigerators. It disappeared by 1930 when it was replaced by CH3Cl. Dichloroethylene
(Dielene or Dieline) was used by Carrier in centrifugal compressors in 1922-26.

1.3.1.1. Domestic refrigeration systems:

      The domestic refrigerator using natural ice (domestic ice box) was invented in 1803
and was used for almost 150 years without much alteration. The domestic ice box used to be
made of wood with suitable insulation. Ice used to be kept at the top of the box, and low
temperatures are produced in the box due to heat transfer from ice by natural convection. A
drip pan is used to collect the water formed due to the melting of ice. The box has to be
replenished with fresh ice once all the ice melts. Though the concept is quite simple, the
domestic ice box suffered from several disadvantages. The user has to replenish the ice as


                                            7               Version 1 ME, IIT Kharagpur
soon as it is consumed, and the lowest temperatures that could be produced inside the
compartment are limited. In addition, it appears that warm winters caused severe shortage of
natural ice in USA. Hence, efforts, starting from 1887 have been made to develop domestic
refrigerators using mechanical systems. The initial domestic mechanical refrigerators were
costly, not completely automatic and were not very reliable. However, the development of
mechanical household refrigerators on a large scale was made possible by the development of
small compressors, automatic refrigerant controls, better shaft seals, developments in
electrical power systems and induction motors. General Electric Company introduced the first
domestic refrigerator in 1911, followed by Frigidaire in 1915. Kelvinator launched the
domestic mechanical refrigerator in 1918 in USA. In 1925, USA had about 25 million
domestic refrigerators of which only 75000 were mechanical. However, the manufacture of
domestic refrigerators grew very rapidly, and by 1949 about 7 million domestic refrigerators
were produced annually. With the production volumes increasing the price fell sharply (the
price was 600 dollars in 1920 and 155 dollars in 1940). The initial domestic refrigerators used
mainly sulphur dioxide as refrigerant. Some units used methyl chloride and methylene
chloride. These refrigerants were replaced by Freon-12 in 1930s. In the beginning these
refrigerators were equipped with open type compressors driven by belt drive. General
Electric Company introduced the first refrigerator with a hermetic compressor in 1926. Soon
the open type compressors were completely replaced by the hermetic compressors. First
refrigerators used water-cooled condensers, which were soon replaced by air cooled-
condensers. Though the development of mechanical domestic refrigerators was very rapid in
USA, it was still rarely used in other countries. In 1930 only rich families used domestic
refrigerators in Europe. The domestic refrigerator based on absorption principle as proposed
by Platen and Munters, was first made by Electrolux Company in 1931 in Sweden. In Japan
the first mechanical domestic refrigerator was made in 1924. The first dual temperature
(freezer-refrigerator) domestic refrigerator was introduced in 1939. The use of mechanical
domestic refrigerators grew rapidly all over the world after the Second World War. Today, a
domestic refrigerator has become an essential kitchen appliance not only in highly developed
countries but also in countries such as India. Except very few almost all the present day
domestic refrigerators are mechanical refrigerators that use a hermetic compressor and an air
cooled condenser. The modern refrigerators use either HFC-134a (hydro-fluoro-carbon) or
iso-butane as refrigerant.

1.3.1.2. Air conditioning systems:

        Refrigeration systems are also used for providing cooling and dehumidification in
summer for personal comfort (air conditioning). The first air conditioning systems were used
for industrial as well as comfort air conditioning. Eastman Kodak installed the first air
conditioning system in 1891 in Rochester, New York for the storage of photographic films.
An air conditioning system was installed in a printing press in 1902 and in a telephone
exchange in Hamburg in 1904. Many systems were installed in tobacco and textile factories
around 1900. The first domestic air conditioning system was installed in a house in Frankfurt
in 1894. A private library in St Louis, USA was air conditioned in 1895, and a casino was air
conditioned in Monte Carlo in 1901. Efforts have also been made to air condition passenger
rail coaches using ice. The widespread development of air conditioning is attributed to the
American scientist and industrialist Willis Carrier. Carrier studied the control of humidity in
1902 and designed a central air conditioning plant using air washer in 1904. Due to the
pioneering efforts of Carrier and also due to simultaneous development of different
components and controls, air conditioning quickly became very popular, especially after
1923. At present comfort air conditioning is widely used in residences, offices, commercial
buildings, air ports, hospitals and in mobile applications such as rail coaches, automobiles,


                                              8               Version 1 ME, IIT Kharagpur
aircrafts etc. Industrial air conditioning is largely responsible for the growth of modern
electronic, pharmaceutical, chemical industries etc. Most of the present day air conditioning
systems use either a vapour compression refrigeration system or a vapour absorption
refrigeration system. The capacities vary from few kilowatts to megawatts.

        Figure 1.3 shows the basic components of a vapour compression refrigeration system.
As shown in the figure the basic system consists of an evaporator, compressor, condenser and
an expansion valve. The refrigeration effect is obtained in the cold region as heat is extracted
by the vaporization of refrigerant in the evaporator. The refrigerant vapour from the
evaporator is compressed in the compressor to a high pressure at which its saturation
temperature is greater than the ambient or any other heat sink. Hence when the high pressure,
high temperature refrigerant flows through the condenser, condensation of the vapour into
liquid takes place by heat rejection to the heat sink. To complete the cycle, the high pressure
liquid is made to flow through an expansion valve. In the expansion valve the pressure and
temperature of the refrigerant decrease. This low pressure and low temperature refrigerant
vapour evaporates in the evaporator taking heat from the cold region. It should be observed
that the system operates on a closed cycle. The system requires input in the form of
mechanical work. It extracts heat from a cold space and rejects heat to a high temperature
heat sink.




           Fig.1.3. Schematic of a basic vapour compression refrigeration system
       A refrigeration system can also be used as a heat pump, in which the useful output is
the high temperature heat rejected at the condenser. Alternatively, a refrigeration system can
be used for providing cooling in summer and heating in winter. Such systems have been built
and are available now.




                                               9               Version 1 ME, IIT Kharagpur
Q. Compared to natural refrigeration methods, artificial refrigeration methods are:
a) Continuous
b) Reliable
c) Environment friendly
d) Can work under almost all conditions
Ans. a), b) and d)

Q. In the evaporator of a vapour compression refrigeration system:
a) A low temperature is maintained so that heat can flow from the external fluid
b) Refrigeration effect is produced as the refrigerant liquid vaporizes
c) A low pressure is maintained so that the compressor can run
d) All of the above
Ans. a) and b)

Q. The function of a compressor in a vapour compression refrigeration system is to:
a) To maintain the required low-side pressure in the evaporator
b) To maintain the required high-side pressure in the condenser
c) To circulate required amount of refrigerant through the system
d) To safeguard the refrigeration system
Ans. a), b) and c)

Q. In a vapour compression refrigeration system, a condenser is primarily required so that:
a) A high pressure can be maintained in the system
b) The refrigerant evaporated in the evaporator can be recycled
c) Performance of the system can be improved
d) Low temperatures can be produced
Ans. b)

Q. The function of an expansion valve is to:
a) Reduce the refrigerant pressure
b) Maintain high and low side pressures
c) Protect evaporator
d) All of the above
Ans. b)

Q. In a domestic icebox type refrigerator, the ice block is kept at the top because:
a) It is convenient to the user
b) Disposal of water is easier
c) Cold air can flow down due to buoyancy effect
d) None of the above
Ans. c)

Q. An air conditioning system employs a refrigeration system to:
a) Cool and dehumidify air supplied to the conditioned space
b) To heat and humidify the air supplied to the conditioned space
c) To circulate the air through the system
d) To purify the supply air
Ans. a)




                                               10               Version 1 ME, IIT Kharagpur
1.3.2. Vapour Absorption Refrigeration Systems:

        John Leslie in 1810 kept H2SO4 and water in two separate jars connected together.
H2SO4 has very high affinity for water. It absorbs water vapour and this becomes the
principle of removing the evaporated water vapour requiring no compressor or pump. H2SO4
is an absorbent in this system that has to be recycled by heating to get rid of the absorbed
water vapour, for continuous operation. Windhausen in 1878 used this principle for
absorption refrigeration system, which worked on H2SO4. Ferdinand Carre invented aqua-
ammonia absorption system in 1860. Water is a strong absorbent of NH3. If NH3 is kept in a
vessel that is exposed to another vessel containing water, the strong absorption potential of
water will cause evaporation of NH3 requiring no compressor to drive the vapours. A liquid
pump is used to increase the pressure of strong solution. The strong solution is then heated in
a generator and passed through a rectification column to separate the water from ammonia.
The ammonia vapour is then condensed and recycled. The pump power is negligible hence;
the system runs virtually on low- grade energy used for heating the strong solution to separate
the water from ammonia. These systems were initially run on steam. Later on oil and natural
gas based systems were introduced. Figure 1.4 shows the essential components of a vapour
absorption refrigeration system. In 1922, Balzar von Platen and Carl Munters, two students at
Royal Institute of Technology, Stockholm invented a three fluid system that did not require a
pump. A heating based bubble pump was used for circulation of strong and weak solutions
and hydrogen was used as a non-condensable gas to reduce the partial pressure of NH3 in the
evaporator. Geppert in 1899 gave this original idea but he was not successful since he was
using air as non-condensable gas. The Platen-Munters refrigeration systems are still widely
used in certain niche applications such as hotel rooms etc. Figure 1.5 shows the schematic of
the triple fluid vapour absorption refrigeration system.




        Fig.1.4. Essential components of a vapour absorption refrigeration system


                                              11              Version 1 ME, IIT Kharagpur
Fig.1.5. Schematic of a triple fluid vapour absorption refrigeration system

       Another variation of vapour absorption system is the one based on Lithium Bromide
(LiBr)-water. This system is used for chilled water air-conditioning system. This is a
descendent of Windhausen’s machine with LiBr replacing H2SO4. In this system LiBr is the
absorbent and water is the refrigerant. This system works at vacuum pressures. The
condenser and the generator are housed in one cylindrical vessel and the evaporator and the
absorber are housed in second vessel. This also runs on low-grade energy requiring a boiler
or process steam.

1.3.3. Solar energy based refrigeration systems:

        Attempts have been made to run vapour absorption systems by solar energy with
concentrating and flat plate solar collectors. Several small solar absorption refrigeration
systems have been made around 1950s in several countries. Professor G.O.G. L f of
America is one of the pioneers in the area of solar refrigeration using flat plate collectors. A
solar refrigeration system that could produce 250 kg of ice per day was installed in Tashkent,
USSR in 1953. This system used a parabolic mirror of 10 m2 area for concentrating the solar
radiation. F. Trombe installed an absorption machine with a cylindro-parabolic mirror of 20
m2 at Montlouis, France, which produced 100 kg of ice per day.

        Serious consideration to solar refrigeration systems was given since 1965, due to the
scarcity of fossil fuel based energy sources. LiBr-water based systems have been developed
for air conditioning purposes. The first solar air conditioning system was installed in an
experimental solar house in University of Queensland, Australia in 1966. After this several
systems based on solar energy were built in many parts of the world including India. In 1976,
there were about 500 solar absorption systems in USA alone. Almost all these were based on
LiBr-water as these systems do not require very high heating temperatures. These systems
were mainly used for space air conditioning.

       Intermittent absorption systems based on solar energy have also been built and
operated successfully. In these systems, the cooling effect is obtained during the nighttime,
while the system gets “charged” during the day using solar energy. Though the efficiency of
these systems is rather poor requiring solar collector area, they may find applications in


                                              12               Version 1 ME, IIT Kharagpur
remote and rural areas where space is not a constraint. In addition, these systems are
environment friendly as they use eco-friendly refrigerants and run on clean and renewable
solar energy.

        Solar adsorption refrigeration system with ammoniacates, sodium thiocyanate,
activated charcoal, zeolite as adsorbents and ammonia, alcohols or fluorocarbons as
refrigerants have also been in use since 1950s. These systems also do not require a
compressor. The refrigerant vapour is driven by the adsorption potential of the adsorbent
stored in an adsorbent bed. This bed is connected to an evaporator/condenser, which consists
of the pure refrigerant. In intermittent adsorption systems, during the night the refrigerant
evaporates and is adsorbed in activated charcoal or zeolite providing cooling effect. During
daytime the adsorbent bed absorbs solar radiation and drives off the refrigerant stored in the
bed. This refrigerant vapour condenses in the condenser and stored in a reservoir for
nighttime use. Thus this simple system consists of an adsorbent bed and a heat exchanger,
which acts as a condenser during the nighttime and, as an evaporator during the night. Pairs
of such reactors can be used for obtaining a continuous cooling

Q. Compared to the compression systems, vapour absorption refrigeration systems:
a) Are environment friendly
b) Use low-grade thermal energy for operation
c) Cannot be used for large capacity refrigeration systems
d) Cannot be used for small capacity refrigeration systems
Ans. a) and b)
Q. In absorption refrigeration systems, the compressor of vapour compression systems is
replaced by:
a) Absorber
b) Generator
c) Pump
d) All of the above
Ans. d)
Q. In a triple fluid vapour absorption refrigeration system, the hydrogen gas is used to:
a) Improve system performance
b) Reduce the partial pressure of refrigerant in evaporator
c) Circulate the refrigerant
d) Provide a vapour seal
Ans. b)
Q. Solar energy based refrigeration systems are developed to:
a) Reduce fossil fuel consumption
b) Provide refrigeration in remote areas
c) Produce extremely low temperatures
d) Eliminate compressors
Ans. a) and b)
Q. Solar energy based refrigeration systems:
a) Cannot be used for large capacity systems
b) Cannot be made continuous
c) Are not environment friendly
d) None of the above
Ans. d)




                                             13               Version 1 ME, IIT Kharagpur
1.3.4. Gas Cycle Refrigeration:

        If air at high pressure expands and does work (say moves a piston or rotates a
turbine), its temperature will decrease. This fact is known to man as early as the 18th century.
Dalton and Gay Lusaac studied this in 1807. Sadi Carnot mentioned this as a well-known
phenomenon in 1824. However, Dr. John Gorrie a physician in Florida developed one such
machine in 1844 to produce ice for the relief of his patients suffering from fever. This
machine used compressed air at 2 atm. pressure and produced brine at a temperature of –7oC,
which was then used to produce ice. Alexander Carnegie Kirk in 1862 made an air cycle
cooling machine. This system used steam engine to run its compressor. Using a compression
ratio of 6 to 8, Kirk could produce temperatures as low as 40oC. Paul Gifford in 1875
perfected the open type of machine. This machine was further improved by T B Lightfoot, A
Haslam, Henry Bell and James Coleman. This was the main method of marine refrigeration
for quite some time. Frank Allen in New York developed a closed cycle machine employing
high pressures to reduce the volume flow rates. This was named dense air machine. These
days air cycle refrigeration is used only in aircrafts whose turbo compressor can handle large
volume flow rates. Figure 1.6 shows the schematic of an open type air cycle refrigeration
system. The basic system shown here consists of a compressor, an expander and a heat
exchanger. Air from the cold room is compressed in the compressor. The hot and high
pressure air rejects heat to the heat sink (cooling water) in the heat exchanger. The warm but
high pressure air expands in the expander. The cold air after expansion is sent to the cold
room for providing cooling. The work of expansion partly compensates the work of
compression; hence both the expander and the compressor are mounted on a common shaft.




        Fig.1.6. Schematic of a basic, open type air cycle refrigeration system




                                              14               Version 1 ME, IIT Kharagpur
1.3.5. Steam Jet Refrigeration System:

        If water is sprayed into a chamber where a low pressure is maintained, a part of the
water will evaporate. The enthalpy of evaporation will cool the remaining water to its
saturation temperature at the pressure in the chamber. Obviously lower temperature will
require lower pressure. Water freezes at 0oC hence temperature lower than 4oC cannot be
obtained with water. In this system, high velocity steam is used to entrain the evaporating
water vapour. High-pressure motive steam passes through either convergent or convergent-
divergent nozzle where it acquires either sonic or supersonic velocity and low pressure of the
order of 0.009 kPa corresponding to an evaporator temperature of 4oC. The high momentum
of motive steam entrains or carries along with it the water vapour evaporating from the flash
chamber. Because of its high velocity it moves the vapours against the pressure gradient up to
the condenser where the pressure is 5.6-7.4 kPa corresponding to condenser temperature of
35-45oC. The motive vapour and the evaporated vapour both are condensed and recycled.
This system is known as steam jet refrigeration system. Figure 1.7 shows a schematic of the
system. It can be seen that this system requires a good vacuum to be maintained. Sometimes,
booster ejector is used for this purpose. This system is driven by low- grade energy that is
process steam in chemical plants or a boiler.




                  Fig.1.7. Schematic of a steam jet refrigeration system

         In 1838, the Frenchman Pelletan was granted a patent for the compression of steam by
means of a jet of motive steam. Around 1900, the Englishman Charles Parsons studied the
possibility of reduction of pressure by an entrainment effect from a steam jet. However, the
credit for constructing the steam jet refrigeration system goes to the French engineer, Maurice
Leblanc who developed the system in 1907-08. In this system, ejectors were used to produce
a high velocity steam jet (≈ 1200 m/s). Based on Leblanc’s design the first commercial
system was made by Westinghouse in 1909 in Paris. Even though the efficiency of the steam
jet refrigeration system was low, it was still attractive as water is harmless and the system can
run using exhaust steam from a steam engine. From 1910 onwards, stem jet refrigeration


                                               15               Version 1 ME, IIT Kharagpur
systems were used mainly in breweries, chemical factories, warships etc. In 1926, the French
engineer Follain improved the machine by introducing multiple stages of vaporization and
condensation of the suction steam. Between 1928-1930, there was much interest in this type
of systems in USA. In USA they were mainly used for air conditioning of factories, cinema
theatres, ships and even railway wagons. Several companies such as Westinghouse, Ingersoll
Rand and Carrier started commercial production of these systems from 1930. However,
gradually these systems were replaced by more efficient vapour absorption systems using
LiBr-water. Still, some east European countries such as Czechoslovakia and Russia
manufactured these systems as late as 1960s. The ejector principle can also be used to
provide refrigeration using fluids other than water, i.e., refrigerants such as CFC-11, CFC-21,
CFC-22, CFC-113, CFC-114 etc. The credit for first developing these closed vapour jet
refrigeration systems goes to the Russian engineer, I.S. Badylkes around 1955. Using
refrigerants other than water, it is possible to achieve temperatures as low as –100oC with a
single stage of compression. The advantages cited for this type of systems are simplicity and
robustness, while difficult design and economics are its chief disadvantages.


1.3.6. Thermoelectric Refrigeration Systems:

        In 1821 the German physicist T.J. Seebeck reported that when two junctions of
dissimilar metals are kept at two different temperatures, an electro motive force (emf) is
developed, resulting in flow of electric current. The emf produced is found to be proportional
to temperature difference. In 1834, a Frenchmen, J. Peltier observed the reverse effect, i.e.,
cooling and heating of two junctions of dissimilar materials when direct current is passed
through them, the heat transfer rate being proportional to the current. In 1838, H.F.E. Lenz
froze a drop of water by the Peltier effect using antimony and bismuth (it was later found that
Lenz could freeze water as the materials used were not pure metals but had some impurities
in them). In 1857, William Thomson (Lord Kelvin) proved by thermodynamic analysis that
Seebeck effect and Peltier effect are related and he discovered another effect called Thomson
effect after his name. According to this when current flows through a conductor of a
thermocouple that has an initial temperature gradient in it, then heat transfer rate per unit
length is proportional to the product of current and the temperature. As the current flow
through thermoelectric material it gets heated due to its electrical resistance. This is called the
Joulean effect, further, conduction heat transfer from the hot junction to the cold junction
transfers heat. Both these heat transfer rates have to be compensated by the Peltier Effect for
some useful cooling to be produced. For a long time, thermoelectric cooling based on the
Peltier effect remained a laboratory curiosity as the temperature difference that could be
obtained using pure metals was too small to be of any practical use. Insulating materials give
poor thermoelectric performance because of their small electrical conductivity while metals
are not good because of their large thermal conductivity. However, with the discovery of
semiconductor materials in 1949-50, the available temperature drop could be increased
considerably, giving rise to commercialization of thermoelectric refrigeration systems. Figure
1.8 shows the schematic of the thermoelectric refrigeration system based on semiconductor
materials. The Russian scientist, A. F. Ioffe is one of the pioneers in the area of
thermoelectric refrigeration systems using semiconductors. Several domestic refrigerators
based on thermoelectric effect were made in USSR as early as 1949. However, since 1960s
these systems are used mainly used for storing medicines, vaccines etc and in electronic
cooling. Development also took place in many other countries. In USA domestic
refrigerators, air conditioners, water coolers, air conditioned diving suits etc. were made




                                                16               Version 1 ME, IIT Kharagpur
12V
                Fig. 1.8. Schematic of a thermoelectric refrigeration system
using these effects. System capacities were typically small due to poor efficiency. However
some large refrigeration capacity systems such as a 3000 kcal/h air conditioner and a 6 tonne
capacity cold storage were also developed. By using multistaging temperatures as low as –
145oC were obtained. These systems due to their limited performance (limited by the
materials) are now used only in certain niche applications such as electronic cooling, mobile
coolers etc. Efforts have also been made to club thermoelectric systems with photovoltaic
cells with a view to develop solar thermoelectric refrigerators.


1.3.7. Vortex tube systems:

        In 1931, the French engineer Georges Ranque (1898-1973) discovered an interesting
phenomenon, which is called “Ranque effect” or “vortex effect”. The tangential injection of
air into a cylindrical tube induces to quote his words “ a giratory expansion with
simultaneous production of an escape of hot air and an escape of cold air”. Ranque was
granted a French patent in 1928 and a US patent in 1934 for this effect. However, the
discovery was neglected until after the second world war, when in 1945, Rudolph Hilsch, a
German physicist, studied this effect and published a widely read scientific paper on this
device. Thus, the vortex tube has also been known as the "Ranque-Hilsch Tube”. Though the
efficiency of this system is quite low, it is very interesting due to its mechanical simplicity
and instant cooling. It is convenient where there is a supply of compressed air. The present
day vortex tube uses compressed air as a power source, it has no moving parts, and produces
hot air from one end and cold air from the other. The volume and temperature of these two
airstreams are adjustable with a valve built into the hot air exhaust. Temperatures as low as
−46°C and as high as 127°C are possible. Compressed air is supplied to the vortex tube and
passes through nozzles that are tangential to an internal counter bore. These nozzles set the
air in a vortex motion. This spinning stream of air turns 90° and passes down the hot tube in
the form of a spinning shell, similar to a tornado. A valve at one end of the tube allows some
of the warmed air to escape. What does not escape, heads back down the tube as a second
vortex inside the low-pressure area of the larger vortex. This inner vortex loses heat and
exhausts through the other end as cold air. Currently vortex tube is used for spot cooling of
machine parts, in electronic cooling and also in cooling jackets for miners, firemen etc.




                                              17              Version 1 ME, IIT Kharagpur
Q. In an air cycle refrigeration system, low temperatures are produced due to:

a) Evaporation of liquid air
b) Throttling of air
c) Expansion of air in turbine
d) None of the above
Ans. c)

Q. Air cycle refrigeration systems are most commonly used in:

a) Domestic refrigerators
b) Aircraft air conditioning systems
c) Cold storages
d) Car air conditioning systems
Ans. b)

Q. The required input to the steam jet refrigeration systems is in the form of:

a) Mechanical energy
b) Thermal energy
c) High pressure, motive steam
d) Both mechanical and thermal energy
Ans. c)

Q. A nozzle is used in steam jet refrigeration systems to:

a) To convert the high pressure motive steam into high velocity steam
b) To reduce energy consumption
c) To improve safety aspects
d) All of the above
Ans. a)

Q. The materials used in thermoelectric refrigeration systems should have:

a) High electrical and thermal conductivity
b) High electrical conductivity and low thermal conductivity
c) Low electrical conductivity and high thermal conductivity
c) Low electrical and thermal conductivity
Ans. b)

Q. A thermoelectric refrigeration systems requires:

a) A high voltage AC (alternating current) input
b) A low voltage AC input
c) A high voltage DC (direct current) input
d) A low voltage DC input
Ans. d).




                                               18               Version 1 ME, IIT Kharagpur
1.3.8. Summary:

        In this lecture the student is introduced to different methods of refrigeration, both
natural and artificial. Then a brief history of artificial refrigeration techniques is presented
with a mention of the pioneers in this field and important events. The working principles of
these systems are also described briefly. In subsequent chapters the most important of these
refrigeration systems will be discussed in detail.

Questions:

Q. Explain why ice making using nocturnal cooling is difficult on nights when the sky is
cloudy?

Ans. In order to make ice from water, water has to be first sensibly cooled from its initial
temperature to its freezing point (0oC) and then latent heat has to be transferred at 0oC. This
requires a heat sink that is at a temperature lower than 0oC. Ice making using nocturnal
cooling relies on radiative heat transfer from the water to the sky (which is at about 55oC)
that acts as a heat sink. When the sky is cloudy, the clouds reflect most of the radiation back
to earth and the effective surface temperature of clouds is also much higher. As a result,
radiative heat transfer from the water becomes very small, making the ice formation difficult.

Q. When you add sufficient amount of glucose to a glass of water, the water becomes cold. Is
it an example of refrigeration, if it is, can this method be used for devising a refrigeration
system?

Ans. Yes, this is an example of refrigeration as the temperature of glucose solution is lower
than the surroundings. However, this method is not viable, as the production of refrigeration
continuously requires an infinite amount of water and glucose or continuous recovery of
glucose from water.

Q. To what do you attribute the rapid growth of refrigeration technology over the last
century?

Ans. The rapid growth of refrigeration technology over the last century can be attributed to
several reasons, some of them are:

i. Growing global population leading to growing demand for food, hence, demand for better
food processing and food preservation methods. Refrigeration is required for both food
processing and food preservation (Food Chain)
ii. Growing demand for refrigeration in almost all industries
iii. Growing demand for comfortable conditions (air conditioned) at residences, workplaces
etc.
iv. Rapid growth of technologies required for manufacturing various refrigeration
components
v. Availability of electricity, and
vi. Growing living standards




                                              19               Version 1 ME, IIT Kharagpur
Lesson
                         2
History Of Refrigeration –
         Development Of
        Refrigerants And
            Compressors

            1    Version 1 ME, IIT Kharagpur
The objectives of the present lesson are to introduce the student to the
history of refrigeration in terms of:
1. Refrigerant development (Section 2.2):

          i.        Early refrigerants (Section 2.2.1)
          ii.       Synthetic fluorocarbon based refrigerants (Section 2.2.2)
          iii.      Non-ozone depleting refrigerants (Section 2.2.3)

2. Compressor development (Section 2.3):

   i.            Low-speed steam engine driven compressors (Section 2.3.1)
   ii.           High-speed electric motor driven compressors (Section 2.3.1)
   iii.          Rotary vane and rolling piston compressors (Section 2.3.2)
   iv.           Screw compressors (Section 2.3.2)
   v.            Scroll compressors (Section 2.3.2)
   vi.           Centrifugal compressors (Section 2.3.3)

At the end of the lesson the student should be able to:

          i.        State the importance of refrigerant selection
          ii.       List various refrigerants used before the invention of CFCs
          iii.      List various CFC refrigerants and their impact on refrigeration
          iv.       State the environmental issues related to the use of CFCs
          v.        State the refrigerant development after Montreal protocol
          vi.       List important compressor types
          vii.      List important landmarks in the development of compressors

2.1. Introduction:
        The development of refrigeration and air conditioning industry depended to a large
extent on the development of refrigerants to suit various applications and the development of
various system components. At present the industry is dominated by the vapour compression
refrigeration systems, even though the vapour absorption systems have also been developed
commercially. The success of vapour compression refrigeration systems owes a lot to the
development of suitable refrigerants and compressors. The theoretical thermodynamic
efficiency of a vapour compression system depends mainly on the operating temperatures.
However, important practical issues such as the system design, size, initial and operating
costs, safety, reliability, and serviceability etc. depend very much on the type of refrigerant
and compressor selected for a given application. This lesson presents a brief history of
refrigerants and compressors. The emphasis here is mainly on vapour compression
refrigeration systems, as these are the most commonly used systems, and also refrigerants and
compressors play a critical role here. The other popular type of refrigeration system, namely
the vapour absorption type has seen fewer changes in terms of refrigerant development, and
relatively less number of problems exist in these systems as far as the refrigerants are
concerned.



                                                   2               Version 1 ME, IIT Kharagpur
2.2. Refrigerant development – a brief history
        In general a refrigerant may be defined as “any body or substance that acts as a
cooling medium by extracting heat from another body or substance”. Under this general
definition, many bodies or substances may be called as refrigerants, e.g. ice, cold water, cold
air etc. In closed cycle vapour compression, absorption systems, air cycle refrigeration
systems the refrigerant is a working fluid that undergoes cyclic changes. In a thermoelectric
system the current carrying electrons may be treated as a refrigerant. However, normally by
refrigerants we mean the working fluids that undergo condensation and evaporation as in
compression and absorption systems. The history that we are talking about essentially refers
to these substances. Since these substances have to evaporate and condense at required
temperatures (which may broadly lie in the range of –100oC to +100oC) at reasonable
pressures, they have to be essentially volatile. Hence, the development of refrigerants started
with the search for suitable, volatile substances. Historically the development of these
refrigerants can be divided into three distinct phases, namely:

   i.      Refrigerants prior to the development of CFCs
   ii.     The synthetic fluorocarbon (FC) based refrigerants
   iii.    Refrigerants in the aftermath of stratospheric ozone layer depletion

2.2.1. Refrigerants prior to the development of CFCs

        Water is one of the earliest substances to be used as a refrigerant, albeit not in a closed
system. Production of cold by evaporation of water dates back to 3000 B.C. Archaeological
findings show pictures of Egyptian slaves waving fans in front of earthenware jars to
accelerate the evaporation of water from the porous surfaces of the pots, thereby producing
cold water. Of course, the use of “punkahs” for body cooling in hot summer is very well
known in countries like India. Production of ice by nocturnal cooling is also well known.
People also had some knowledge of producing sub-zero temperatures by the use of
“refrigerant mixtures”. It is believed that as early as 4th Century AD people in India were
using mixtures of salts (sodium nitrate, sodium chloride etc) and water to produce
temperatures as low as –20oC. However, these natural refrigeration systems working with
water have many limitations and hence were confined to a small number of applications.

        Water was the first refrigerant to be used in a continuous refrigeration system by
William Cullen (1710-1790) in 1755. William Cullen is also the first man to have
scientifically observed the production of low temperatures by evaporation of ethyl ether in
1748. Oliver Evans (1755-1819) proposed the use of a volatile fluid in a closed cycle to
produce ice from water. He described a practical system that uses ethyl ether as the
refrigerant. As already mentioned the credit for building the first vapour compression
refrigeration system goes to Jakob Perkins (1766-1849). Perkins used sulphuric (ethyl) ether
obtained from India rubber as refrigerant. Early commercial refrigerating machines
developed by James Harrison (1816-1893) also used ethyl ether as refrigerant. Alexander
Twining (1801-1884) also developed refrigerating machines using ethyl ether. After these
developments, ethyl ether was used as refrigerant for several years for ice making, in
breweries etc. Ether machines were gradually replaced by ammonia and carbon dioxide based
machines, even though they were used for a longer time in tropical countries such as India.




                                                3                Version 1 ME, IIT Kharagpur
Ethyl ether appeared to be a good refrigerant in the beginning, as it was easier to handle it
since it exists as a liquid at ordinary temperatures and atmospheric pressure. Ethyl ether has a
normal boiling point (NBP) of 34.5oC, this indicates that in order to obtain low temperatures,
the evaporator pressure must be lower than one atmosphere, i.e., operation in vacuum.
Operation of a system in vacuum may lead to the danger of outside air leaking into the
system resulting in the formation of a potentially explosive mixture. On the other hand a
relatively high normal boiling point indicates lower pressures in the condenser, or for a given
pressure the condenser can be operated at higher condensing temperatures. This is the reason
behind the longer use of ether in tropical countries with high ambient temperatures.
Eventually due to the high NBP, toxicity and flammability problems ethyl ether was replaced
by other refrigerants. Charles Tellier (1828-1913) introduced dimethyl ether (NBP =
   23.6oC) in 1864. However, this refrigerant did not become popular, as it is also toxic and
inflammable.

        In 1866, the American T.S.C. Lowe (1832-1913) introduced carbon dioxide
compressor. However, it enjoyed commercial success only in 1880s due largely to the efforts
of German scientists Franz Windhausen (1829-1904) and Carl von Linde (1842-1934).
Carbon dioxide has excellent thermodynamic and thermophysical properties, however, it has
a low critical temperature (31.7oC) and very high operating pressures. Since it is non-
flammable and non-toxic it found wide applications principally for marine refrigeration. It
was also used for refrigeration applications on land. Carbon dioxide was used successfully for
about sixty years however, it was completely replaced by CFCs. It is ironic to note that ever
since the problem of ozone layer depletion was found, carbon dioxide is steadily making a
comeback by replacing the synthetic CFCs/HCFCs/HFCs etc.

         One of the landmark events in the history of refrigerants is the introduction of
ammonia. The American David Boyle (1837-1891) was granted the first patent for ammonia
compressor in 1872. He made the first single acting vertical compressor in 1873. However,
the credit for successfully commercializing ammonia systems goes to Carl von Linde (1842-
1934) of Germany, who introduced these compressors in Munich in 1876. Linde is credited
with perfecting the ammonia refrigeration technology and owing to his pioneering efforts;
ammonia has become one of the most important refrigerants to be developed. Ammonia has a
NBP of       33.3oC, hence, the operating pressures are much higher than atmospheric.
Ammonia has excellent thermodynamic and thermophysical properties. It is easily available
and inexpensive. However, ammonia is toxic and has a strong smell and slight flammability.
In addition, it is not compatible with some of the common materials of construction such as
copper. Though these are considered to be some of its disadvantages, ammonia has stood the
test of time and the onslaught of CFCs due to its excellent properties. At present ammonia is
used in large refrigeration systems (both vapour compression and vapour absorption) and also
in small absorption refrigerators (triple fluid vapour absorption).

        In 1874, Raoul Pictet (1846-1929) introduced sulphur dioxide (NBP= 10.0oC).
Sulphur dioxide was an important refrigerant and was widely used in small refrigeration
systems such as domestic refrigerators due to its small refrigerating effect. Sulphur dioxide
has the advantage of being an auto-lubricant. In addition it is not only non-flammable, but
actually acts as a flame extinguisher. However, in the presence of water vapour it produces
sulphuric acid, which is highly corrosive. The problem of corrosion was overcome by an
airtight sealed compressor (both motor and compressor are mounted in the same outer



                                               4               Version 1 ME, IIT Kharagpur
casing). However, after about sixty years of use in appliances such as domestic refrigerators,
sulphur dioxide was replaced by CFCs.

       In addition to the above, other fluids such as methyl chloride, ethyl chloride, iso-
butane, propane, ethyl alcohol, methyl and ethyl amines, carbon tetra chloride, methylene
chloride, gasoline etc. were tried but discarded due to one reason or other.

2.2.2. The synthetic CFCs/HCFCs:

        Almost all the refrigerants used in the early stages of refrigeration suffered from one
problem or other. Most of these problems were linked to safety issues such as toxicity,
flammability, high operating pressures etc. As a result large-scale commercialization of
refrigeration systems was hampered. Hence it was felt that “refrigeration industry needs a
new refrigerant if they expect to get anywhere”. The task of finding a “safe” refrigerant was
taken up by the American Thomas Midgley, Jr., in 1928. Midgley was already famous for the
invention of tetra ethyl lead, an important anti-knock agent for petrol engines. Midgley along
with his associates Albert L. Henne and Robert R. McNary at the Frigidaire Laboratories
(Dayton, Ohio, USA) began a systematic study of the periodic table. From the periodic table
they quickly eliminated all those substances yielding insufficient volatility. They then
eliminated those elements resulting in unstable and toxic gases as well as the inert gases,
based on their very low boiling points. They were finally left with eight elements: carbon,
nitrogen, oxygen, sulphur, hydrogen, fluorine, chlorine and bromine. These eight elements
clustered at an intersecting row and column of the periodic table, with fluorine at the
intersection. Midgley and his colleagues then made three interesting observations:

   i.      Flammability decreases from left to right for the eight elements
   ii.     Toxicity generally decreases from the heavy elements at the bottom to the lighter
           elements at the top
   iii.    Every known refrigerant at that time was made from the combination of those
           eight “Midgley” elements.

    A look at the refrigerants discussed above shows that all of them are made up of seven
out of the eight elements identified by Midgley (fluorine was not used till then). Other
researchers have repeated Midgley’s search with more modern search methods and databases,
but arrived at the same conclusions (almost all the currently used refrigerants are made up of
Midgley elements, only exception is Iodine, studies are being carried out on refrigerants
containing iodine in addition to some of the Midgley elements). Based on their study,
Midgely and his colleagues have developed a whole range of new refrigerants, which are
obtained by partial replacement of hydrogen atoms in hydrocarbons by fluorine and chlorine.
They have shown how fluorination and chlorination of hydrocarbons can be varied to obtain
desired boiling points (volatility) and also how properties such as toxicity, flammability are
influenced by the composition. The first commercial refrigerant to come out of Midgley’s
study is Freon-12 in 1931. Freon-12 with a chemical formula CCl2F2, is obtained by replacing
the four atoms of hydrogen in methane (CH4) by two atoms of chlorine and two atoms of
fluorine. Freon-12 has a normal boiling point of 29.8oC, and is one of the most famous and
popular synthetic refrigerants. It was exclusively used in small domestic refrigerators, air
conditioners, water coolers etc for almost sixty years. Freon-11 (CCl3F) used in large
centrifugal air conditioning systems was introduced in 1932. This is followed by Freon-22
(CHClF2) and a whole series of synthetic refrigerants to suit a wide variety of applications.



                                              5               Version 1 ME, IIT Kharagpur
Due to the emergence of a large number of refrigerants in addition to the existence of the
older refrigerants, it has become essential to work out a numbering system for refrigerants.
Thus all refrigerants were indicated with ‘R’ followed by a unique number (thus Freon-12 is
changed to R12 etc). The numbering of refrigerants was done based on certain guidelines. For
all synthetic refrigerants the number (e.g. 11, 12, 22) denotes the chemical composition. The
number of all inorganic refrigerants begins with ‘7’ followed by their molecular weight. Thus
R-717 denotes ammonia (ammonia is inorganic and its molecular weight is 17), R-718
denotes water etc.. Refrigerant mixtures begin with the number 4 (zeotropic) or 5
(azeotropic), e.g. R-500, R-502 etc.

        The introduction of CFCs and related compounds has revolutionized the field of
refrigeration and air conditioning. Most of the problems associated with early refrigerants
such as toxicity, flammability, and material incompatibility were eliminated completely.
Also, Freons are highly stable compounds. In addition, by cleverly manipulating the
composition a whole range of refrigerants best suited for a particular application could be
obtained. In addition to all this, a vigorous promotion of these refrigerants as “wonder gases”
and “ideal refrigerants” saw rapid growth of Freons and equally rapid exit of conventional
refrigerants such as carbon dioxide, sulphur dioxide etc. Only ammonia among the older
refrigerants survived the Freon magic. The Freons enjoyed complete domination for about
fifty years, until the Ozone Layer Depletion issue was raised by Rowland and Molina in
1974. Rowland and Molina in their now famous theory argued that the highly stable
chlorofluorocarbons cause the depletion of stratospheric ozone layer. Subsequent studies and
observations confirmed Rowland and Molina theory on stratospheric ozone depletion by
chlorine containing CFCs. In view of the seriousness of the problem on global scale, several
countries have agreed to ban the harmful Ozone Depleting Substances, ODS (CFCs and
others) in a phase-wise manner under Montreal Protocol. Subsequently almost all countries of
the world have agreed to the plan of CFC phase-out. In addition to the ozone layer depletion,
the CFCs and related substances were also found to contribute significantly to the problem of
“global warming”. This once again brought the scientists back to the search for “safe”
refrigerants. The “safety” now refers to not only the immediate personal safety issues such as
flammability, toxicity etc., but also the long-term environmental issues such as ozone layer
depletion and global warming.

2.2.3. Refrigerants in the aftermath of Ozone Layer Depletion:

        The most important requirement for refrigerants in the aftermath of ozone layer
depletion is that it should be a non-Ozone Depleting Substance (non-ODS). Out of this
requirement two alternatives have emerged. The first one is to look for zero ODP synthetic
refrigerants and the second one is to look for “natural” substances. Introduction of
hydrofluorocarbons (HFCs) and their mixtures belong to the first route, while the re-
introduction of carbon dioxide (in a supercritical cycle), water and various hydrocarbons and
their mixtures belong to the second route. The increased use of ammonia and use of other
refrigeration cycles such as air cycle refrigeration systems and absorption systems also come
under the second route. Both these routes have found their proponents and opponents. HFC-
134a (synthetic substance) and hydrocarbons (natural substances) have emerged as
alternatives to Freon-12. No clear pure fluid alternative has been found as yet for the other
popular refrigerant HCFC-22. However several mixtures consisting of synthetic and natural
refrigerants are being used and suggested for future use. Table 2.1 shows the list of
refrigerants being replaced and their alternatives. Mention must be made here about the other



                                              6               Version 1 ME, IIT Kharagpur
environmental problem, global warming. In general the non-ODS synthetic refrigerants such
as HFC-134a have high global warming potential (GWP), hence they face an uncertain
future. Since the global warming impact of a refrigerant also depends on the energy
efficiency of the system using the refrigerant (indirect effect), the efficiency issue has become
important in the design of new refrigeration systems. Though the issues of ozone layer
depletion and global warming has led to several problems, they have also had beneficial
effects of making people realize the importance of environmental friendliness of
technologies. It is expected that with the greater awareness more responsible designs will
emerge which will ultimately benefit the whole mankind.




                  Table 2.1. Candidate refrigerants for replacing CFCs


                                               7                Version 1 ME, IIT Kharagpur
Q. Ethyl ether was the first refrigerant to be used commercially, because:
a) It exists as liquid at ambient conditions
b) It is safe
c) It is inexpensive
d) All of the above
Ans. a)
Q. Ammonia is one of the oldest refrigerants, which is still used widely, because:
a) It offers excellent performance
b) It is a natural refrigerant
c) It is inexpensive
d) All of the above
Ans. d)
Q. In the olden days Carbon dioxide was commonly used in marine applications as:
a) It has low critical temperature
b) Its operating pressures are high
c) It is non-toxic and non-flammable
d) It is odorless
Ans. c)
Q. Sulphur dioxide was mainly used in small refrigeration systems, because:
a) It is non-toxic and non-flammable
b) It has small refrigeration effect
c) It is expensive
d) It was easily available
Ans. b)
Q. Need for synthetic refrigerants was felt, as the available natural refrigerants:
a) Were not environment friendly
b) Suffered from several perceived safety issues
c) Were expensive
d) Were inefficient
Ans. b)
Q. The synthetic CFC based refrigerants were developed by:
a) Partial replacement of hydrogen atoms in hydrocarbons by chlorine, fluorine etc.
b) Modifying natural refrigerants such as carbon dioxide, ammonia
c) Modifying inorganic compounds by adding carbon, fluorine and chlorine
d) Mixing various hydrocarbons
Ans. a)
Q. The synthetic refrigerants were extremely popular as they are:
a) Environment friendly
b) Mostly non-toxic and non-flammable
c) Chemically stable
d) Inexpensive
Ans. b) and c)
Q. CFC based refrigerants are being replaced as they are found to:
a) Cause ozone layer depletion
b) Consume more energy
c) React with several materials of construction
d) Expensive
Ans. a)




                                             8               Version 1 ME, IIT Kharagpur
2.3. Compressor development – a brief history
       Compressor may be called as a heart of any vapour compression system. The rapid
development of refrigeration systems is made possible due to the developments in
compressor technologies.

2.3.1. Reciprocating compressors:

        The earliest compressor used by Jakob Perkins is a hand-operated compressor, very
much like a hand operated pump used for pumping water. Harrison also used a hand-operated
ether compressor in 1850, but later used steam engine driven compressors in commercial
machines. A small half horsepower (hp) compressor was used as early as 1857 to produce 8
kg of ice per hour. Three other machines with 8 to 10 hp were in use in England in 1858. In
1859, the firm P.N. Russel of Australia undertook the manufacture of Harrison’s machines,
the first compressors to be made with two vertical cylinders. The firm of Siebe brothers of
England went on perfecting the design of the early compressors. Their first compressors were
vertical and the later were horizontal. From 1863 to 1870, Ferdinand Carre of France took out
several patents on diaphragm compressors, valves etc.

       Charles Tellier used a horizontal single cylinder methyl ether compressor in 1863.
These compressors were initially installed in a chocolate factory near Paris and in a brewery
in USA in 1868. In 1876 the ship “Le Frigorifique” was equipped with three of Tellier’s
methyl ether compressors and successfully transported chilled meat from Rouen in France to
Buenos Ayres in Argentina (a distance of 12000 km).

        T.S.C. Lowe (1832-1913) started making carbon dioxide compressors in 1865, and
began to use them in the manufacture of ice from 1868. However, the credit for perfecting the
design of carbon dioxide compressor goes to Franz Windhausen of Germany in 1886. The
British firm J&E Hall began the commercial production of carbon dioxide compressors in
1887. They started manufacturing two-stage carbon dioxide compressors since 1889. Soon
the carbon dioxide systems replaced air cycle refrigeration systems in ships. Several firms
started manufacturing these compressors on a large scale. This trend continued upto the
Second World War.

        A significant development took place in 1876 by the introduction of a twin cylinder
vertical compressor working with ammonia by Carl von Linde. Similar to his earlier methyl
ether compressor (1875) a bath of liquid mercury was used to make the compressor gas-tight.
This ammonia compressor was installed in a brewery in 1877 and worked there till 1908. In
1877, Linde improved the compressor design by introducing a horizontal, double acting
cylinder with a stuffing box made from two packings separated by glycerine (glycerine was
later replaced by mineral oil). Figure 2.1 shows the schematic of Linde’s horizontal, double
acting compressor. This design became very successful, and was a subject of many patents.
Several manufacturers in other countries adopted this design and manufactured several of
these compressors. USA began the production of ammonia compressors on a large scale from
1880.

         Raoul Pictet invented the sulphur dioxide compressor in 1874. The machine was
initially built in Geneva, then in Paris and afterwards in some other countries. The
compressor developed by Pictet was horizontal and was not lubricated as sulphur dioxide acts



                                             9               Version 1 ME, IIT Kharagpur
Fig.2.1. Schematic of Linde’s horizontal, double acting compressor


       as an auto-lubricant. As mentioned before, the sulphur dioxide system was an instant
success and was used for almost sixty years, especially in small systems.

      In 1878, methyl chloride system was introduced by Vincent in France. The French
company Crespin & Marteau started manufacturing methyl chloride compressors from 1884.
This continued upto the first world war. Escher Wyss of USA started making these
compressors from 1913 onwards, right upto the Second World War.

        At the beginning of 20th century, practically all the compressors in USA, Great Britain
and Germany used either ammonia or carbon dioxide. In France, in addition to these two,
sulphur dioxide and methyl chloride were also used. Compressor capacity comparison tests
have been conducted on different types of compressors as early as 1887 in Munich, Germany.
Stetefeld in 1904 concluded that there was no marked difference in the performance of
ammonia, carbon dioxide and sulphur dioxide compressors.

        Due to many similarities, the early compressors resembled steam engines in many
ways. Like early steam engines, they were double acting (compression takes place on both
sides of the piston). Both vertical and horizontal arrangements were used, the former being
popular in Europe while the later was popular in USA. A stuffing box arrangement with oil in
the gap was used to reduce refrigerant leakage. The crosshead, connecting rod, crank and
flywheel were in the open. Initially poppet valves were used, which were later changed to
ring-plate type. The cylinder diameters were very large by the present day standards,
typically around 500 mm with stroke lengths of the order of 1200 mm. The rotational speeds
were low (~ 50 rpm), hence the clearances were small, often less than 0.5 % of the swept
volume. Due to generous valve areas and low speed the early compressors were able to
compress mixture of vapour as well as liquid. Slowly, the speed of compressors have been
increased, for example for a 300 kW cooling capacity system, the mean speed was 40 rpm in
1890, 60 in 1900, 80 in 1910, 150 to 160 in 1915, and went upto 220 in 1916. The term “high
speed” was introduced in 1915 for compressors with speeds greater than 150 rpm. However,
none of the compressors of this period exceeded speeds of 500 rpm. However, compressors
of very large capacities (upto 7 MW cooling capacity) were successfully built and operated
by this time. In 1905 the American engineer G.T. Voorhees introduced a dual effect
compressor, which has a supplementary suction orifice opened during compression so that
refrigerant can be taken in at two different pressures. As mentioned, the first two-stage
carbon dioxide compressor was made in 1889 by J&E Hall of England. Sulzer Company
developed the first two-stage ammonia compressor in 1889. York Company of USA made a
two-stage ammonia compressor in 1892.




                                              10              Version 1 ME, IIT Kharagpur
About 1890, attention was focused on reducing the clearance space between the
piston and cylinder head (clearance space) in order to increase the capacity of the
compressors. Attention was also focused on the design of stuffing box and sealing between
piston and cylinder to reduce refrigerant leakage. In 1897 the Belgian manufacturer Bruno
Lebrun introduced a rotary stuffing box, which was much easier to seal than the reciprocating
one. A rotating crankshaft enclosed in a crankcase drove the two opposed horizontal
cylinders. Many studies were also conducted on compressor valves as early as 1900. By
1910, the heavy bell valves were replaced by much lighter, flat valves. By about 1900, the
design of stuffing box for large compressors was almost perfected. However, for smaller
compressors the energy loss due to friction at the stuffing box was quiet high. This fact gave
rise to the idea of sealed or hermetic compressor (both compressor and motor are mounted in
the same enclosure). However, since the early electric motors with brushes and commutator
and primitive insulation delayed the realization of hermetic compressors upto the end of First
World War.

        As mentioned, the earliest compressors were hand operated. Later they were driven by
steam engines. However, the steam engines gradually gave way to electric motors. Diesel and
petrol engine driven compressors were developed much later. In USA, 90% of the motive
power was provided by the steam engine in 1914, 71% in 1919, 43% in 1922 and 32% in
1924. This trend continued and slowly the steam engine driven compressors have become
almost obsolete. Between 1914 and 1920, the electric motor was considered to be the first
choice for refrigerant compressors.

       About 1920, high-speed compressors (with speeds greater than 500 rpm) began to
appear in the market. The horizontal, double acting compressors were gradually replaced by
multi-cylinder, vertical, uni-flow compressors in V- and W- arrangement, the design being
adopted from automobile engine design. In 1937, an American compressor (Airtemp)
comprised two groups of 7 cylinders arranged radially at both ends of 1750 rpm electric
motor. These changes resulted in a reduction of size and weight of compressor, for example,
a York 300 000 kcal/h compressor had the following characteristics:

 Year   Refrigerant    No. of cylinders   Speed (rpm)   Cooling capacity per unit weight
1910    NH3            2 cylinders        70          6.5 kcal/h per kg
1940    NH3            4 cylinders        400         42 kcal/h per kg
1975    R22            16 cylinders in    1750        200 kcal/h per kg
                       W-arrangement

        All the compressors developed in the early stages are of “open” type. In the open type
compressors the compressor and motor are mounted separately. The driving shaft of the
motor and the crankshaft of the compressor are connected either by a belt drive or a gear
drive. With the open type compressors there is always a possibility of refrigerant leakage
from an open type compressor, even though the rotating mechanical seals developed reduced
the leakage rate considerably. Since leakage cannot be eliminated completely, systems
working with open type compressors require periodic servicing and maintenance. Since it is
difficult to provide continuous maintenance on small systems (e.g. domestic refrigerators),
serious thought was given to tackle this problem. A hermetic or sealed compressor was the
outcome of this.




                                             11               Version 1 ME, IIT Kharagpur
An Australian Douglas Henry Stokes made the first sealed or hermetic compressor in
1918. Hermetic compressors soon became extremely popular, and the rapid development of
small hermetic compressors has paved the way for taking the refrigeration systems to the
households. With the capacitor starting of the electric motor becoming common in 1930s, the
design of hermetic compressors was perfected. In 1926, General Electric Co. of USA
introduced the domestic refrigerator working with a hermetic compressor. Initially 4-pole
motors were used. After 1940 the 4-pole motors were replaced by 2-pole motors, which
reduced of the compressor unit significantly. Soon the 2-pole hermetic refrigerant compressor
became universal. Gradually, the capacity of hermetic compressors was increased. Now-a -
days hermetic compressors are available for refrigerating capacities starting from a few Watts
to kilowatts. At present, due to higher efficiency and serviceability, the open type
compressors are used in medium to large capacity systems, whereas the hermetic
compressors are exclusively used in small capacity systems on a mass production. The
currently available hermetic compressors are compact and extremely reliable. They are
available for a wide variety of refrigerants and applications. Figure 2.2 shows cut view of a
hermetic compressor.




                        Fig.2.2. Cut view of a hermetic compressor
Other types of compressors:

2.3.2.Positive displacement type (other than reciprocating):

       In 1919, the French engineer Henri Corblin (1867-1947) patented a diaphragm
compressor, in which the alternating movement of a diaphragm produced the suction and
compression effects. Initially these compressors were used for liquefying chlorine, but later
were used in small to medium capacity systems working with ammonia, carbon dioxide etc.

       Several types of rotary air compressors existed before the First World War, and this
idea has soon been extended to refrigerants. However, they became popular with the
introduction of Freons in 1930s. The first positive displacement, rotary vane compressor
using methyl chloride was installed on an American ship “Carnegie”. However, a practical



                                             12                Version 1 ME, IIT Kharagpur
positive displacement, rotary vane compressor could only be developed in 1920. In Germany,
F.Stamp made an ethyl chloride compressor of 1000 kcal/h capacity. In USA, Sunbeam
Electric made small sulphur dioxide based rotary sliding vane compressors of 150 kcal/h
capacity, rotating at 1750 rpm for domestic refrigerators. In 1922, Sulzer, Switzerland made
“Frigorotor” of 1000 to 10000 kcal/h using methyl chloride. Sulzer later extended this design
to ammonia for large capacities (“Frigocentrale”). Escher Wyss, also of Switzerland rotary
sliding vane compressor “Rotasco” in 1936. These compressors were also made by Lebrun,
Belgium in 1924 and also by Grasso (Netherlands).

        A model of the rolling piston type compressor was made in 1919 in France. This
compressor was improved significantly by W.S.F. Rolaff of USA in 1920 and M. Guttner of
Germany in 1922. Rolaff’s design was first tried on a sulphur dioxide based domestic
refrigerator. Guttner’s compressors were used with ammonia and methyl chloride in large
commercial installations. Hermetic, rolling piston type compressors were made in USA by
Frigidaire for refrigerant R114, by General Electric for ethyl formate and by Bosch in
Germany for sulphur dioxide. In 1931, Vilter of USA made large rotary compressors (200000
kcal/h) first for ammonia and then for R12.

        At present, positive displacement rotary compressors based on sliding vane and
rolling piston types are used in small to medium capacity applications all over the world.
These compressors offer the advantages of compactness, efficiency, low noise etc. However,
these compressors require very close manufacturing tolerances as compared to reciprocating
compressors. Figure 2.3 shows the schematic of a rolling piston compressor. The low
pressure refrigerant from the evaporator enters into the compressor from the port on the right
hand side, it gets compressed due to the rotation of the rolling piston and leaves the
compressor from the discharge valve on the left hand side.




               Fig.2.3. Schematic of a rolling piston type, rotary compressor

       The screw compressor is another important type of positive displacement compressor.
The screw compressors entered into refrigeration market in 1958, even though the basic idea
goes back to 1934, by A. Lysholm of Sweden. The screw compressors are of twin-screw



                                             13               Version 1 ME, IIT Kharagpur
(two helical rotors) type or a single-screw (single rotor) type. The twin-screw compressor
uses a pair of intermeshing rotors instead of a piston to produce compression. The rotors
comprise of helical lobes fixed to a shaft. One rotor is called the male rotor and it will
typically have four bulbous lobes. The other rotor is the female rotor and this has valleys
machined into it that match the curvature of the male lobes. Typically the female rotor will
have six valleys. This means that for one revolution of the male rotor, the female rotor will
only turn through 240 deg. For the female rotor to complete one cycle, the male rotor will
have to rotate 11/2 times. The single screw type compressor was first made for air in 1967.
Grasso, Netherlands introduced single screw refrigerant compressors in 1974. The screw
compressor (both single and twin screw) became popular since 1960 and its design has
almost been perfected. Presently it is made for medium to large capacity range for ammonia
and fluorocarbon based refrigerants. It competes with the reciprocating compressors at the
lower capacity range and on the higher capacity side it competes with the centrifugal
compressor. Due to the many favorable performance characteristics, screw compressors are
taking larger and larger share of refrigerant compressor market. Figure 2.4 shows the
photograph of a cut, semi-hermetic, single-screw compressor.




             Fig.2.4. Cut view of a semi-hermetic, single-screw compressor

        The scroll compressor is one of the more recent but important types of positive
displacement compressors. It uses the compression action provided by two intermeshing
scrolls - one fixed and the other orbiting. This orbital movement draws gas into the
compression chamber and moves it through successively smaller “pockets” formed by the
scroll’s rotation, until it reaches maximum pressure at the center of the chamber. There, it’s
released through a discharge port in the fixed scroll. During each orbit, several pockets are
compressed simultaneously, so operation is virtually continuous. Figure 2.5 shows gas flow
pattern in a scroll compressor and Fig.2.6 shows the photograph of a Copeland scroll
compressor. The principle of the scroll compressor was developed during the early 1900's and
was patented for the first time in 1905. Although the theory for the scroll compressor
indicated a machine potentially capable of reasonably good efficiencies, at that time the
technology simply didn't exist to accurately manufacture the scrolls. It was almost 65 years
later that the concept was re-invented by a refrigeration industry keen to exploit the potentials



                                               14               Version 1 ME, IIT Kharagpur
of scroll technology. Copeland in USA, Hitachi in Japan introduced the scroll type of
  compressors for refrigerants in 1980s. Scroll compressors have been developed for operating
  temperatures in the range of 45°C to +5°C suitable for cold storage and air conditioning
  applications. This scroll has also been successfully applied throughout the world in many
  freezer applications. Today, scroll compressors are very popular due to the high efficiency,
  which results from higher compression achieved at a lower rate of leakage. They are
  available in cooling capacities upto 50 kW. They are quiet in operation and compact.
  However, the manufacturing of scroll compressors is very complicated due to the extremely
  close tolerances to be maintained for proper operation of the compressor.




                                                   Fig.2.6. Photograph of a cut scroll
                                                        compressor (Copeland)




                                              15                 Version 1 ME, IIT Kharagpur
Fig.2.5. Gas flow in a scroll
compressor
2.3.3. Dynamic type:

        Centrifugal compressors (also known as turbocompressors) belong to the class of
dynamic type of compressors, in which the pressure rise takes place due to the exchange of
angular momentum between the rotating blades and the vapour trapped in between the blades.
Centrifugal were initially used for compressing air. The development of these compressors is
largely due to the efforts of Auguste Rateau of France from 1890. In 1899, Rateau developed
single impeller (rotor) and later multi-impeller fans. Efforts have been made to use similar
compressors for refrigeration. In 1910, two Germans H. Lorenz and E. Elgenfeld proposed
the use of centrifugal compressors for refrigeration at the International Congress of
Refrigeration, Vienna. However, it was Willis H. Carrier, who has really laid the foundation
of centrifugal compressors for air conditioning applications in 1911. The motivation for
developing centrifugal compressors originated from the fact that the reciprocating
compressors were slow and bulky, especially for large capacity systems. Carrier wanted to
develop a more compact system working with non-flammable, non-toxic and odorless
refrigerant. In 1919, he tried a centrifugal compressor with dichloroethylene (C2H2Cl2) and
then dichloromethane (CCl2H2). In 1926 he used methyl chloride, and in 1927 he had nearly
50 compressors working with dichloroethylene. The centrifugal compressors really took-off
with the introduction of Freons in 1930s. Refrigerant R11 was the refrigerant chosen by
Carrier for his centrifugal compressor based air conditioning systems in 1933. Later his
company developed centrifugal compressors working with R12, propane and other
refrigerants for use in low temperature applications. In Switzerland, Brown Boveri Co.
developed ammonia based centrifugal compressors as early as 1926. Later they also
developed large centrifugal compressors working with Freons. Till 1950, the centrifugal
compressors were used mainly in USA for air conditioning applications. However,
subsequently centrifugal compressors have become industry standard for large refrigeration
and air conditioning applications all over the world. Centrifugal compressors developed
before 1940, had 5 to 6 stages, while they had 2 to 3 stages between 1940 to 1960. After
1960, centrifugal compressors with a single stage were also developed. Subsequently,
compact, hermetic centrifugal compressor developed for medium to large capacity
applications. The large diameter, 3600 rpm machines were replaced by compact 10000 to
12000 rpm compressors. Large centrifugal compressors of cooling capacities in the range of
200000 kcal/h to 2500000 kcal/h were used in places such as World Trade Centre, New
York. Figure 2.7 shows cut-view of a two-stage, semi-hermetic centrifugal compressor.




           Fig. 2.7 Cut-view of a two-stage, semi-hermetic centrifugal compressor.


                                            16              Version 1 ME, IIT Kharagpur
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp
Refrigeration and-air-conditioning-by-iit-kgp

Contenu connexe

Tendances

Presentation on rankine cycle
Presentation on rankine cyclePresentation on rankine cycle
Presentation on rankine cycleManan Neupane
 
Simple Vapor Absorption Refrigeration System
Simple Vapor Absorption Refrigeration SystemSimple Vapor Absorption Refrigeration System
Simple Vapor Absorption Refrigeration SystemIan Louise Celestino
 
Refrigeration and Heat Pump Systems
Refrigeration and Heat Pump SystemsRefrigeration and Heat Pump Systems
Refrigeration and Heat Pump SystemsSalman Jailani
 
Power Plants and Basic Thermodynamic Cycles
Power Plants and Basic Thermodynamic CyclesPower Plants and Basic Thermodynamic Cycles
Power Plants and Basic Thermodynamic CyclesSalman Haider
 
THERMOACOUSTIC REFRIGERATION
THERMOACOUSTIC REFRIGERATIONTHERMOACOUSTIC REFRIGERATION
THERMOACOUSTIC REFRIGERATIONNimalan_I
 
Refrigeration and air conditioning
Refrigeration and air conditioningRefrigeration and air conditioning
Refrigeration and air conditioningEagle .
 
Heat Exchanger recuperators
Heat Exchanger  recuperators  Heat Exchanger  recuperators
Heat Exchanger recuperators Ali Abdullah
 
Duct sizing methods and filter types
Duct sizing methods and filter typesDuct sizing methods and filter types
Duct sizing methods and filter typesSANKA_SILVA
 
Basics of refrigeration engineering section b
Basics of refrigeration engineering  section bBasics of refrigeration engineering  section b
Basics of refrigeration engineering section bAkshit Kohli
 
J2006 termodinamik 1 unit9
J2006 termodinamik 1 unit9J2006 termodinamik 1 unit9
J2006 termodinamik 1 unit9Malaysia
 
Engineering applications of thermodynamics
Engineering applications of thermodynamicsEngineering applications of thermodynamics
Engineering applications of thermodynamicsNisarg Amin
 
Air refrigeration system by Bell Coleman cycle and Vortex tube
Air refrigeration system by Bell Coleman cycle and Vortex tubeAir refrigeration system by Bell Coleman cycle and Vortex tube
Air refrigeration system by Bell Coleman cycle and Vortex tubeaparnamalyala
 
Air refrigerationsystem
Air refrigerationsystemAir refrigerationsystem
Air refrigerationsystemnaphis ahamad
 
Heat Exchanger Pressure Drop Analysis
Heat Exchanger Pressure Drop AnalysisHeat Exchanger Pressure Drop Analysis
Heat Exchanger Pressure Drop AnalysisRushikesh Bidve
 
Refrigeration and airconditioning
Refrigeration and airconditioningRefrigeration and airconditioning
Refrigeration and airconditioningHarsh Gandhi
 

Tendances (20)

Presentation on rankine cycle
Presentation on rankine cyclePresentation on rankine cycle
Presentation on rankine cycle
 
Simple Vapor Absorption Refrigeration System
Simple Vapor Absorption Refrigeration SystemSimple Vapor Absorption Refrigeration System
Simple Vapor Absorption Refrigeration System
 
Heat transfer
Heat transferHeat transfer
Heat transfer
 
Refrigeration and Heat Pump Systems
Refrigeration and Heat Pump SystemsRefrigeration and Heat Pump Systems
Refrigeration and Heat Pump Systems
 
Power Plants and Basic Thermodynamic Cycles
Power Plants and Basic Thermodynamic CyclesPower Plants and Basic Thermodynamic Cycles
Power Plants and Basic Thermodynamic Cycles
 
THERMOACOUSTIC REFRIGERATION
THERMOACOUSTIC REFRIGERATIONTHERMOACOUSTIC REFRIGERATION
THERMOACOUSTIC REFRIGERATION
 
Heat conduction through a plane wall
Heat conduction through a plane wallHeat conduction through a plane wall
Heat conduction through a plane wall
 
Refrigeration and air conditioning
Refrigeration and air conditioningRefrigeration and air conditioning
Refrigeration and air conditioning
 
Heat Exchanger recuperators
Heat Exchanger  recuperators  Heat Exchanger  recuperators
Heat Exchanger recuperators
 
Heat 4e chap11_lecture
Heat 4e chap11_lectureHeat 4e chap11_lecture
Heat 4e chap11_lecture
 
Duct sizing methods and filter types
Duct sizing methods and filter typesDuct sizing methods and filter types
Duct sizing methods and filter types
 
Basics of refrigeration engineering section b
Basics of refrigeration engineering  section bBasics of refrigeration engineering  section b
Basics of refrigeration engineering section b
 
J2006 termodinamik 1 unit9
J2006 termodinamik 1 unit9J2006 termodinamik 1 unit9
J2006 termodinamik 1 unit9
 
Evaporators
EvaporatorsEvaporators
Evaporators
 
Engineering applications of thermodynamics
Engineering applications of thermodynamicsEngineering applications of thermodynamics
Engineering applications of thermodynamics
 
Fundamentals of Heat Pipes With Applications and Types
Fundamentals of Heat Pipes With Applications and TypesFundamentals of Heat Pipes With Applications and Types
Fundamentals of Heat Pipes With Applications and Types
 
Air refrigeration system by Bell Coleman cycle and Vortex tube
Air refrigeration system by Bell Coleman cycle and Vortex tubeAir refrigeration system by Bell Coleman cycle and Vortex tube
Air refrigeration system by Bell Coleman cycle and Vortex tube
 
Air refrigerationsystem
Air refrigerationsystemAir refrigerationsystem
Air refrigerationsystem
 
Heat Exchanger Pressure Drop Analysis
Heat Exchanger Pressure Drop AnalysisHeat Exchanger Pressure Drop Analysis
Heat Exchanger Pressure Drop Analysis
 
Refrigeration and airconditioning
Refrigeration and airconditioningRefrigeration and airconditioning
Refrigeration and airconditioning
 

En vedette

Refrigeration And Air Conditioning
Refrigeration And Air ConditioningRefrigeration And Air Conditioning
Refrigeration And Air ConditioningSaurabh Jain
 
Refrigeration and-air-conditioning-notes
Refrigeration and-air-conditioning-notesRefrigeration and-air-conditioning-notes
Refrigeration and-air-conditioning-notesOlumide Daniel
 
refrigeration and air conditioning
refrigeration and air conditioningrefrigeration and air conditioning
refrigeration and air conditioningGear Abohar
 
Refrigeration and air conditioning ppt
Refrigeration and air conditioning pptRefrigeration and air conditioning ppt
Refrigeration and air conditioning pptShubham Hadadare
 
Air conditioning and refrigeration. mechanical engineering handbook
Air conditioning and refrigeration. mechanical engineering handbookAir conditioning and refrigeration. mechanical engineering handbook
Air conditioning and refrigeration. mechanical engineering handbookmazgan
 
REFRIGERATION SYSTEM
REFRIGERATION SYSTEMREFRIGERATION SYSTEM
REFRIGERATION SYSTEMDenny John
 
40 lessons on refrigeration and air conditioning yr2008 p809
40 lessons on refrigeration and air conditioning yr2008 p80940 lessons on refrigeration and air conditioning yr2008 p809
40 lessons on refrigeration and air conditioning yr2008 p809Nikolay Mavrodiev
 
Cold storage ppt pragati
Cold storage ppt pragatiCold storage ppt pragati
Cold storage ppt pragatiPragati Singham
 
Refrigeration and Air conditioning
Refrigeration and Air conditioningRefrigeration and Air conditioning
Refrigeration and Air conditioningSLA1987
 
Refrigration & air conditioning
Refrigration & air conditioningRefrigration & air conditioning
Refrigration & air conditioningSiddharth Bedarker
 
Refrigeration and air conditioning
Refrigeration and air conditioningRefrigeration and air conditioning
Refrigeration and air conditioningManiz Joshi
 
Air refrigeration system used in aircraft
Air refrigeration system used in aircraftAir refrigeration system used in aircraft
Air refrigeration system used in aircraftNissan Patel
 
Refrigeration system (1)
Refrigeration system (1)Refrigeration system (1)
Refrigeration system (1)Prakash Kumawat
 
Basics Refrigeration Fundamentals
Basics Refrigeration FundamentalsBasics Refrigeration Fundamentals
Basics Refrigeration Fundamentalspawansher2002
 
Refrigeration cycle
Refrigeration cycleRefrigeration cycle
Refrigeration cyclezubi0585
 
Basic refrigeration cycle
Basic refrigeration  cycleBasic refrigeration  cycle
Basic refrigeration cycleNina Maulani
 

En vedette (20)

Refrigeration And Air Conditioning
Refrigeration And Air ConditioningRefrigeration And Air Conditioning
Refrigeration And Air Conditioning
 
Refrigeration and-air-conditioning-notes
Refrigeration and-air-conditioning-notesRefrigeration and-air-conditioning-notes
Refrigeration and-air-conditioning-notes
 
refrigeration and air conditioning
refrigeration and air conditioningrefrigeration and air conditioning
refrigeration and air conditioning
 
Refrigeration and air conditioning ppt
Refrigeration and air conditioning pptRefrigeration and air conditioning ppt
Refrigeration and air conditioning ppt
 
Air conditioning and refrigeration. mechanical engineering handbook
Air conditioning and refrigeration. mechanical engineering handbookAir conditioning and refrigeration. mechanical engineering handbook
Air conditioning and refrigeration. mechanical engineering handbook
 
REFRIGERATION SYSTEM
REFRIGERATION SYSTEMREFRIGERATION SYSTEM
REFRIGERATION SYSTEM
 
40 lessons on refrigeration and air conditioning yr2008 p809
40 lessons on refrigeration and air conditioning yr2008 p80940 lessons on refrigeration and air conditioning yr2008 p809
40 lessons on refrigeration and air conditioning yr2008 p809
 
Cold storage ppt pragati
Cold storage ppt pragatiCold storage ppt pragati
Cold storage ppt pragati
 
Refrigeration and Air conditioning
Refrigeration and Air conditioningRefrigeration and Air conditioning
Refrigeration and Air conditioning
 
Refrigration & air conditioning
Refrigration & air conditioningRefrigration & air conditioning
Refrigration & air conditioning
 
HVAC Basic Concepts of Air Conditioning
HVAC Basic Concepts of Air ConditioningHVAC Basic Concepts of Air Conditioning
HVAC Basic Concepts of Air Conditioning
 
Refrigeration and air conditioning
Refrigeration and air conditioningRefrigeration and air conditioning
Refrigeration and air conditioning
 
Air refrigeration system used in aircraft
Air refrigeration system used in aircraftAir refrigeration system used in aircraft
Air refrigeration system used in aircraft
 
Refrigeration system (1)
Refrigeration system (1)Refrigeration system (1)
Refrigeration system (1)
 
Basics Refrigeration Fundamentals
Basics Refrigeration FundamentalsBasics Refrigeration Fundamentals
Basics Refrigeration Fundamentals
 
Refrigeration systems
Refrigeration systemsRefrigeration systems
Refrigeration systems
 
Refrigeration cycle
Refrigeration cycleRefrigeration cycle
Refrigeration cycle
 
Basic refrigeration cycle
Basic refrigeration  cycleBasic refrigeration  cycle
Basic refrigeration cycle
 
Air conditioning system
Air conditioning systemAir conditioning system
Air conditioning system
 
Marine Refrigeration and Air Conditioning
Marine Refrigeration and Air ConditioningMarine Refrigeration and Air Conditioning
Marine Refrigeration and Air Conditioning
 

Similaire à Refrigeration and-air-conditioning-by-iit-kgp

refrigeration-air-conditioning-training ppt
refrigeration-air-conditioning-training pptrefrigeration-air-conditioning-training ppt
refrigeration-air-conditioning-training pptnagendran25
 
5022-RAC MODULE-1.pdf
5022-RAC MODULE-1.pdf5022-RAC MODULE-1.pdf
5022-RAC MODULE-1.pdfAthulUdayan2
 
ammonia water (NH3-H2o) diffusion vapor absorption refrigeration system
ammonia water (NH3-H2o) diffusion vapor absorption refrigeration systemammonia water (NH3-H2o) diffusion vapor absorption refrigeration system
ammonia water (NH3-H2o) diffusion vapor absorption refrigeration systemJagannath1234
 
Evaluation of thermal performance of a typical vapor compression refrigeratio...
Evaluation of thermal performance of a typical vapor compression refrigeratio...Evaluation of thermal performance of a typical vapor compression refrigeratio...
Evaluation of thermal performance of a typical vapor compression refrigeratio...Saif al-din ali
 
Cem 350 hvac air side systems 10-2016
Cem 350 hvac air side systems 10-2016Cem 350 hvac air side systems 10-2016
Cem 350 hvac air side systems 10-2016miresmaeil
 
PERFORMANCE EVALUATION AND OPTIMIZATION OF AIR PREHEATER IN THERMAL POWER PLANT
PERFORMANCE EVALUATION AND OPTIMIZATION OF AIR PREHEATER IN THERMAL POWER PLANTPERFORMANCE EVALUATION AND OPTIMIZATION OF AIR PREHEATER IN THERMAL POWER PLANT
PERFORMANCE EVALUATION AND OPTIMIZATION OF AIR PREHEATER IN THERMAL POWER PLANTIAEME Publication
 
Se prod thermo_chapter_5_refrigeration
Se prod thermo_chapter_5_refrigerationSe prod thermo_chapter_5_refrigeration
Se prod thermo_chapter_5_refrigerationVJTI Production
 
DOC-20231017-WA0003..pptx
DOC-20231017-WA0003..pptxDOC-20231017-WA0003..pptx
DOC-20231017-WA0003..pptxKarthik029CSK
 
Compressor and compressed air systems.pptx
Compressor and compressed air systems.pptxCompressor and compressed air systems.pptx
Compressor and compressed air systems.pptxMadan Karki
 
Cooling applications of solar system ppt
Cooling applications of solar system pptCooling applications of solar system ppt
Cooling applications of solar system pptvikramdangi
 
EME Module 3 REFRIGERATION AND AIR CONDITIONING PART-1
EME Module 3 REFRIGERATION AND AIR CONDITIONING  PART-1 EME Module 3 REFRIGERATION AND AIR CONDITIONING  PART-1
EME Module 3 REFRIGERATION AND AIR CONDITIONING PART-1 Rajashekar Matpathi
 
ME8595 – THERMAL ENGINEERING - II
ME8595 – THERMAL ENGINEERING - IIME8595 – THERMAL ENGINEERING - II
ME8595 – THERMAL ENGINEERING - IIprakash0712
 
Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...
Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...
Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...IRJET Journal
 
Fyp presentation (1)
Fyp presentation (1)Fyp presentation (1)
Fyp presentation (1)Imran Mumtaz
 
Fyp presentation (1)
Fyp presentation (1)Fyp presentation (1)
Fyp presentation (1)KayDrive
 
Refrigeration and air conditioning
Refrigeration and air conditioningRefrigeration and air conditioning
Refrigeration and air conditioningVaibhav Tandel
 

Similaire à Refrigeration and-air-conditioning-by-iit-kgp (20)

refrigeration-air-conditioning-training ppt
refrigeration-air-conditioning-training pptrefrigeration-air-conditioning-training ppt
refrigeration-air-conditioning-training ppt
 
5022-RAC MODULE-1.pdf
5022-RAC MODULE-1.pdf5022-RAC MODULE-1.pdf
5022-RAC MODULE-1.pdf
 
ammonia water (NH3-H2o) diffusion vapor absorption refrigeration system
ammonia water (NH3-H2o) diffusion vapor absorption refrigeration systemammonia water (NH3-H2o) diffusion vapor absorption refrigeration system
ammonia water (NH3-H2o) diffusion vapor absorption refrigeration system
 
Evaluation of thermal performance of a typical vapor compression refrigeratio...
Evaluation of thermal performance of a typical vapor compression refrigeratio...Evaluation of thermal performance of a typical vapor compression refrigeratio...
Evaluation of thermal performance of a typical vapor compression refrigeratio...
 
Cem 350 hvac air side systems 10-2016
Cem 350 hvac air side systems 10-2016Cem 350 hvac air side systems 10-2016
Cem 350 hvac air side systems 10-2016
 
PERFORMANCE EVALUATION AND OPTIMIZATION OF AIR PREHEATER IN THERMAL POWER PLANT
PERFORMANCE EVALUATION AND OPTIMIZATION OF AIR PREHEATER IN THERMAL POWER PLANTPERFORMANCE EVALUATION AND OPTIMIZATION OF AIR PREHEATER IN THERMAL POWER PLANT
PERFORMANCE EVALUATION AND OPTIMIZATION OF AIR PREHEATER IN THERMAL POWER PLANT
 
Se prod thermo_chapter_5_refrigeration
Se prod thermo_chapter_5_refrigerationSe prod thermo_chapter_5_refrigeration
Se prod thermo_chapter_5_refrigeration
 
G04563844
G04563844G04563844
G04563844
 
Refrigeration
RefrigerationRefrigeration
Refrigeration
 
DOC-20231017-WA0003..pptx
DOC-20231017-WA0003..pptxDOC-20231017-WA0003..pptx
DOC-20231017-WA0003..pptx
 
Turbin gas
Turbin gas Turbin gas
Turbin gas
 
Compressor and compressed air systems.pptx
Compressor and compressed air systems.pptxCompressor and compressed air systems.pptx
Compressor and compressed air systems.pptx
 
CH-3.pptx
CH-3.pptxCH-3.pptx
CH-3.pptx
 
Cooling applications of solar system ppt
Cooling applications of solar system pptCooling applications of solar system ppt
Cooling applications of solar system ppt
 
EME Module 3 REFRIGERATION AND AIR CONDITIONING PART-1
EME Module 3 REFRIGERATION AND AIR CONDITIONING  PART-1 EME Module 3 REFRIGERATION AND AIR CONDITIONING  PART-1
EME Module 3 REFRIGERATION AND AIR CONDITIONING PART-1
 
ME8595 – THERMAL ENGINEERING - II
ME8595 – THERMAL ENGINEERING - IIME8595 – THERMAL ENGINEERING - II
ME8595 – THERMAL ENGINEERING - II
 
Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...
Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...
Design and Development of Small Scale VAR System by Using Exhaust Gas of IC E...
 
Fyp presentation (1)
Fyp presentation (1)Fyp presentation (1)
Fyp presentation (1)
 
Fyp presentation (1)
Fyp presentation (1)Fyp presentation (1)
Fyp presentation (1)
 
Refrigeration and air conditioning
Refrigeration and air conditioningRefrigeration and air conditioning
Refrigeration and air conditioning
 

Plus de Olumide Daniel

7 weeks to 100 push ups strengthen and sculpt your arms, abs, chest, back and...
7 weeks to 100 push ups strengthen and sculpt your arms, abs, chest, back and...7 weeks to 100 push ups strengthen and sculpt your arms, abs, chest, back and...
7 weeks to 100 push ups strengthen and sculpt your arms, abs, chest, back and...Olumide Daniel
 
The At-one-ment Between God and Man
The At-one-ment Between God and ManThe At-one-ment Between God and Man
The At-one-ment Between God and ManOlumide Daniel
 
The Battle Of Armageddon
The Battle Of ArmageddonThe Battle Of Armageddon
The Battle Of ArmageddonOlumide Daniel
 
Divine Plan Of The Ages
Divine Plan Of The AgesDivine Plan Of The Ages
Divine Plan Of The AgesOlumide Daniel
 
New world translation of the holy scriptures
New world translation of the holy scripturesNew world translation of the holy scriptures
New world translation of the holy scripturesOlumide Daniel
 
Beware of customs that displease god
Beware of customs that displease godBeware of customs that displease god
Beware of customs that displease godOlumide Daniel
 
Heating and-air-conditioning-of-building-faber-and-kell-chapter-14-air-condit...
Heating and-air-conditioning-of-building-faber-and-kell-chapter-14-air-condit...Heating and-air-conditioning-of-building-faber-and-kell-chapter-14-air-condit...
Heating and-air-conditioning-of-building-faber-and-kell-chapter-14-air-condit...Olumide Daniel
 

Plus de Olumide Daniel (10)

7 weeks to 100 push ups strengthen and sculpt your arms, abs, chest, back and...
7 weeks to 100 push ups strengthen and sculpt your arms, abs, chest, back and...7 weeks to 100 push ups strengthen and sculpt your arms, abs, chest, back and...
7 weeks to 100 push ups strengthen and sculpt your arms, abs, chest, back and...
 
The New Creation
The New CreationThe New Creation
The New Creation
 
The At-one-ment Between God and Man
The At-one-ment Between God and ManThe At-one-ment Between God and Man
The At-one-ment Between God and Man
 
The Battle Of Armageddon
The Battle Of ArmageddonThe Battle Of Armageddon
The Battle Of Armageddon
 
Thy Kingdom Come
Thy Kingdom ComeThy Kingdom Come
Thy Kingdom Come
 
English vol 2
English vol 2English vol 2
English vol 2
 
Divine Plan Of The Ages
Divine Plan Of The AgesDivine Plan Of The Ages
Divine Plan Of The Ages
 
New world translation of the holy scriptures
New world translation of the holy scripturesNew world translation of the holy scriptures
New world translation of the holy scriptures
 
Beware of customs that displease god
Beware of customs that displease godBeware of customs that displease god
Beware of customs that displease god
 
Heating and-air-conditioning-of-building-faber-and-kell-chapter-14-air-condit...
Heating and-air-conditioning-of-building-faber-and-kell-chapter-14-air-condit...Heating and-air-conditioning-of-building-faber-and-kell-chapter-14-air-condit...
Heating and-air-conditioning-of-building-faber-and-kell-chapter-14-air-condit...
 

Dernier

Salesforce Miami User Group Event - 1st Quarter 2024
Salesforce Miami User Group Event - 1st Quarter 2024Salesforce Miami User Group Event - 1st Quarter 2024
Salesforce Miami User Group Event - 1st Quarter 2024SkyPlanner
 
Empowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintEmpowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintMahmoud Rabie
 
Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024D Cloud Solutions
 
UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8DianaGray10
 
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Will Schroeder
 
NIST Cybersecurity Framework (CSF) 2.0 Workshop
NIST Cybersecurity Framework (CSF) 2.0 WorkshopNIST Cybersecurity Framework (CSF) 2.0 Workshop
NIST Cybersecurity Framework (CSF) 2.0 WorkshopBachir Benyammi
 
UiPath Community: AI for UiPath Automation Developers
UiPath Community: AI for UiPath Automation DevelopersUiPath Community: AI for UiPath Automation Developers
UiPath Community: AI for UiPath Automation DevelopersUiPathCommunity
 
20230202 - Introduction to tis-py
20230202 - Introduction to tis-py20230202 - Introduction to tis-py
20230202 - Introduction to tis-pyJamie (Taka) Wang
 
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPA
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPAAnypoint Code Builder , Google Pub sub connector and MuleSoft RPA
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPAshyamraj55
 
Linked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesLinked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesDavid Newbury
 
Introduction to Matsuo Laboratory (ENG).pptx
Introduction to Matsuo Laboratory (ENG).pptxIntroduction to Matsuo Laboratory (ENG).pptx
Introduction to Matsuo Laboratory (ENG).pptxMatsuo Lab
 
Designing A Time bound resource download URL
Designing A Time bound resource download URLDesigning A Time bound resource download URL
Designing A Time bound resource download URLRuncy Oommen
 
Videogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfVideogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfinfogdgmi
 
Secure your environment with UiPath and CyberArk technologies - Session 1
Secure your environment with UiPath and CyberArk technologies - Session 1Secure your environment with UiPath and CyberArk technologies - Session 1
Secure your environment with UiPath and CyberArk technologies - Session 1DianaGray10
 
VoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXVoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXTarek Kalaji
 
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019IES VE
 
Building AI-Driven Apps Using Semantic Kernel.pptx
Building AI-Driven Apps Using Semantic Kernel.pptxBuilding AI-Driven Apps Using Semantic Kernel.pptx
Building AI-Driven Apps Using Semantic Kernel.pptxUdaiappa Ramachandran
 
Crea il tuo assistente AI con lo Stregatto (open source python framework)
Crea il tuo assistente AI con lo Stregatto (open source python framework)Crea il tuo assistente AI con lo Stregatto (open source python framework)
Crea il tuo assistente AI con lo Stregatto (open source python framework)Commit University
 
How Accurate are Carbon Emissions Projections?
How Accurate are Carbon Emissions Projections?How Accurate are Carbon Emissions Projections?
How Accurate are Carbon Emissions Projections?IES VE
 

Dernier (20)

Salesforce Miami User Group Event - 1st Quarter 2024
Salesforce Miami User Group Event - 1st Quarter 2024Salesforce Miami User Group Event - 1st Quarter 2024
Salesforce Miami User Group Event - 1st Quarter 2024
 
Empowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintEmpowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership Blueprint
 
Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024
 
UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8
 
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
 
NIST Cybersecurity Framework (CSF) 2.0 Workshop
NIST Cybersecurity Framework (CSF) 2.0 WorkshopNIST Cybersecurity Framework (CSF) 2.0 Workshop
NIST Cybersecurity Framework (CSF) 2.0 Workshop
 
UiPath Community: AI for UiPath Automation Developers
UiPath Community: AI for UiPath Automation DevelopersUiPath Community: AI for UiPath Automation Developers
UiPath Community: AI for UiPath Automation Developers
 
20230202 - Introduction to tis-py
20230202 - Introduction to tis-py20230202 - Introduction to tis-py
20230202 - Introduction to tis-py
 
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPA
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPAAnypoint Code Builder , Google Pub sub connector and MuleSoft RPA
Anypoint Code Builder , Google Pub sub connector and MuleSoft RPA
 
Linked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesLinked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond Ontologies
 
Introduction to Matsuo Laboratory (ENG).pptx
Introduction to Matsuo Laboratory (ENG).pptxIntroduction to Matsuo Laboratory (ENG).pptx
Introduction to Matsuo Laboratory (ENG).pptx
 
Designing A Time bound resource download URL
Designing A Time bound resource download URLDesigning A Time bound resource download URL
Designing A Time bound resource download URL
 
Videogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfVideogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdf
 
Secure your environment with UiPath and CyberArk technologies - Session 1
Secure your environment with UiPath and CyberArk technologies - Session 1Secure your environment with UiPath and CyberArk technologies - Session 1
Secure your environment with UiPath and CyberArk technologies - Session 1
 
20150722 - AGV
20150722 - AGV20150722 - AGV
20150722 - AGV
 
VoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXVoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBX
 
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
IESVE Software for Florida Code Compliance Using ASHRAE 90.1-2019
 
Building AI-Driven Apps Using Semantic Kernel.pptx
Building AI-Driven Apps Using Semantic Kernel.pptxBuilding AI-Driven Apps Using Semantic Kernel.pptx
Building AI-Driven Apps Using Semantic Kernel.pptx
 
Crea il tuo assistente AI con lo Stregatto (open source python framework)
Crea il tuo assistente AI con lo Stregatto (open source python framework)Crea il tuo assistente AI con lo Stregatto (open source python framework)
Crea il tuo assistente AI con lo Stregatto (open source python framework)
 
How Accurate are Carbon Emissions Projections?
How Accurate are Carbon Emissions Projections?How Accurate are Carbon Emissions Projections?
How Accurate are Carbon Emissions Projections?
 

Refrigeration and-air-conditioning-by-iit-kgp

  • 1. 4O LESSONS ON REFRIGERATION AND AIR CONDITIONING FROM IIT KHARAGPUR. USEFUL TRAINING MATERIAL FOR MECHANICAL ENGINEERING STUDENTS/COLLEGE, OR AS REFERENCE FOR ENGINEER. EE IIT, Kharagpur, India 2008
  • 2. Contents: Lesson Page Lesson 1 History Of Refrigeration [Natural Refrigeration ~ Artificial 7 Refrigeration ] Lesson 2 History Of Refrigeration - Development Of Refrigerants And 26 Compressors [ Refrigerant development - a brief history ~ Compressor development - a brief history ] Lesson 3 Applications Of Refrigeration & Air Conditioning [ Application of 44 refrigeration in Food processing, preservation and distribution ~ Applications of refrigeration in chemical and process industries ~ Special applications of refrigeration ~ Application of air conditioning ] Lesson 4 Review of fundamental principles - Thermodynamics : Part I [ 64 Definitions ~ Thermodynamic properties ~ Fundamental laws of Thermodynamics ] Lesson 5 Review of fundamental principles - Thermodynamics : Part II [ 78 Thermodynamic relations ~ Evaluation of thermodynamic properties ~ Thermodynamic processes ] Lesson 6 Review of fundamentals: Fluid flow [ Fluid flow ] 93 Lesson 7 Review of fundamentals: Heat and Mass transfer [ Heat transfer ~ 104 Fundamentals of Mass transfer ~ Analogy between heat, mass and momentum transfer ~ Multimode heat transfer ~ Heat exchangers ] Lesson 8 Methods of producing Low Temperatures [ Sensible cooling by cold 124 medium ~ Endothermic mixing of substances ~ Phase change processes ~ Expansion of Liquids ~ Expansion of gases ~ Thermoelectric Refrigeration ~ Adiabatic demagnetization ] Lesson 9 Air cycle refrigeration systems [ Air Standard Cycle analysis ~ Basic 138 concepts ~ Reversed Carnot cycle employing a gas ~ Ideal reverse Brayton cycle ~ Aircraft cooling systems ]
  • 3. Lesson 10 Vapour Compression Refrigeration Systems [ Comparison 153 between gas cycles and vapor cycles ~ Vapour Compression Refrigeration Systems ~ The Carnot refrigeration cycle ~ Standard Vapour Compression Refrigeration System (VCRS) ~ Analysis of standard vapour compression refrigeration system ] Lesson 11 Vapour Compression Refrigeration Systems: Performance 171 Aspects And Cycle Modifications [ Performance of SSS cycle ~ Modifications to SSS cycle ~ Effect of superheat on system COP ~ Actual VCRS systems ~ Complete vapour compression refrigeration systems ] Lesson 12 Multi-Stage Vapour Compression Refrigeration Systems [ Flash 193 gas removal using flash tank ~ Intercooling in multi-stage compression ~ Multi-stage system with flash gas removal and intercooling ~ Use of flash tank for flash gas removal ~ Use of flash tank for intercooling only ] Lesson 13 Multi-Evaporator And Cascade Systems [ Individual evaporators 213 and a single compressor with a pressure-reducing valve ~ Multi-evaporator system with multi-compression, intercooling and flash gas removal ~ Multi-evaporator system with individual compressors and multiple expansion valves ~ Limitations of multi-stage systems ~ Cascade Systems ] Lesson 14 Vapour Absorption Refrigeration Systems [ Maximum COP of ideal 238 absorption refrigeration system ~ Properties of refrigerant-absorbent mixtures ~ Basic Vapour Absorption Refrigeration System ~ Refrigerant-absorbent combinations for VARS ] Lesson 15 Vapour Absorption Refrigeration Systems Based On Water- 258 Lithium Bromide Pair [ Properties of water-lithium bromide solutions ~ Steady flow analysis of Water-Lithium Bromide Systems ~ Practical problems in water- lithium bromide systems ~ Commercial systems ~ Heat sources for water-lithium bromide systems ~ Minimum heat source temperatures for LiBr-Water systems ~ Capacity control ] Lesson 16 Vapour Absorption Refrigeration Systems Based On Ammonia- 279 Water Pair [ Properties of ammonia-water solutions ~ Basic Steady-Flow Processes with binary mixtures ] Lesson 17 Vapour Absorption Refrigeration Systems Based On Ammonia- 301 Water Pair [ Working principle ~ Principle of rectification column and dephlegmator ~ Steady-flow analysis of the system ~ Pumpless vapour absorption refrigeration systems ~ Solar energy driven sorption systems ~ Comparison between compression and absorption refrigeration systems ]
  • 4. Lesson 18 Refrigeration System Components: Compressors [ Compressors ~ 317 Reciprocating compressors ] Lesson 19 Performance Of Reciprocating Compressors [ Ideal compressor 337 with clearance ~ Actual compression process ~ Capacity control of reciprocating compressors ~ Compressor lubrication ] Lesson 20 Rotary, Positive Displacement Type Compressors [ Rolling piston 361 (fixed vane) type compressors ~ Multiple vane type compressors ~ Characteristics of rotary, vane type compressors ~ Rotary, screw compressors ~ Scroll compressors ] Lesson 21 Centrifugal Compressors [ Analysis of centrifugal compressors ~ 376 Selection of impeller Speed and impeller diameter ~ Refrigerant capacity of centrifugal compressors ~ Performance aspects of centrifugal compressor ~ Commercial refrigeration systems with centrifugal compressors ] Lesson 22 Condensers & Evaporators [ Condensers ~ Classification of 402 condensers ~ Analysis of condensers ~ Optimum condenser pressure for lowest running cost ] Lesson 23 Condensers & Evaporators [ Classification ~ Natural Convection type 439 evaporator coils ~ Flooded Evaporator ~ Shell-and-Tube Liquid Chillers ~ Shell-and- Coil type evaporator ~ Double pipe type evaporator ~ Baudelot type evaporators ~ Direct expansion fin-and-tube type ~ Plate Surface Evaporators ~ Plate type evaporators ~ Thermal design of evaporators ~ Enhancement of heat transfer coefficients ~ Wilson's plot ] Lesson 24 Expansion Devices [ Capillary Tube ~ Automatic Expansion Valve (AEV) 465 ~ Flow Rate through orifice ~ Thermostatic Expansion Valve (TEV) ~ Float type expansion valves ~ Electronic Type Expansion Valve ~ Practical problems in operation of Expansion valves ] Lesson 25 Analysis Of Complete Vapour Compression Refrigeration 504 Systems [ Reciprocating compressor performance characteristics ~ Evaporator Performance ~ Expansion valve Characteristics ~ Condensing unit ~ Performance of complete system - condensing unit and evaporator ~ Effect of expansion valve ] Lesson 26 Refrigerants [ Primary and secondary refrigerants ~ Refrigerant 523 selection criteria ~ Designation of refrigerants ~ Comparison between different refrigerants ]
  • 5. Lesson 27 Psychrometry [ Methods for estimating properties of moist air ~ 537 Measurement of psychrometric properties ~ Calculation of psychrometric properties from p, DBT and WBT ~ Psychrometer ] Lesson 28 Psychrometric Processes [ Important psychrometric processes ~ Air 553 Washers ~ Enthalpy potential ] Lesson 29 Inside And Outside Design Conditions [ Selection of inside design 572 conditions ~ Thermal comfort ~ Heat balance equation for a human being ~ Factors affecting thermal comfort ~ Indices for thermal comfort ~ Predicted Mean Vote (PMV) and Percent People Dissatisfied (PPD) ~ Selection of outside design conditions ] Lesson 30 Psychrometry Of Air Conditioning Systems [ Summer air 591 conditioning systems ~ Guidelines for selection of supply state and cooling coil ] Lesson 31 Evaporative, Winter And All Year Air Conditioning Systems [ 608 Introduction to evaporative air conditioning systems ~ Classification of evaporative cooling systems ~ Advantages and disadvantages of evaporative cooling systems ~ Applicability of evaporative cooling systems ~ Winter Air Conditioning Systems ~ All year (complete) air conditioning systems ~ ] Lesson 32 Cooling And Heating Load Calculations - Estimation Of Solar 626 Radiation [ Solar radiation ~ Calculation of direct, diffuse and reflected radiations ] Lesson 33 Cooling And Heating Load Calculations -Solar Radiation 645 Through Fenestration - Ventilation And Infiltration [ Solar radiation through fenestration ~ Estimation of solar radiation through fenestration ~ Effect of external shading ~ Ventilation for Indoor Air Quality (IAQ) ~ Infiltration ~ Heating and cooling loads due to ventilation and infiltration ] Lesson 34 Cooling And Heating Load Calculations - Heat Transfer Through 660 Buildings - Fabric Heat Gain/Loss [ One-dimensional, steady state heat transfer through buildings ~ Unsteady heat transfer through opaque walls and roofs ~ One- dimensional, unsteady heat transfer through building walls and roof ] Lesson 35 Cooling And Heating Load Calculations - Estimation Of 688 Required Cooling/Heating Capacity [ Heating versus cooling load calculations ~ Methods of estimating cooling and heating loads ~ Cooling load calculations ~ Estimation of the cooling capacity of the system ~ Heating load calculations ~ ]
  • 6. Lesson 36 Selection Of Air Conditioning Systems [ Selection criteria for air 709 conditioning systems ~ Classification of air conditioning systems ~ All water systems ~ Air-water systems ~ Unitary refrigerant based systems ] Lesson 37 Transmission Of Air In Air Conditioning Ducts [ Transmission of air 734 ~ Flow of air through ducts ~ Estimation of pressure loss in ducts ~ Dynamic losses in ducts ~ Static Regain ] Lesson 38 Design Of Air Conditioning Ducts [ General rules for duct design ~ 752 Classification of duct systems ~ Commonly used duct design methods ~ Performance of duct systems ~ System balancing and optimization ~ Fans ] Lesson 39 Space Air Distribution [ Design of air distribution systems ~ Behaviour 772 of free-stream jet ~ Circular jets ~ Types of air distribution devices ~ Return air inlets ~ Airflow patterns inside conditioned space ~ Stratified mixing flow ~ Spot cooling/heating ~ Selection of supply air outlets ] Lesson 40 Ventilation For Cooling [ Natural versus mechanical ventilation ~ 797 Natural ventilation ~ Guidelines for natural ventilation ~ Forced ventilation using electric fans ~ Interior air movement ] Reference books for this course 809
  • 7. Lesson 1 History Of Refrigeration 1 Version 1 ME, IIT Kharagpur
  • 8. Objectives of the lesson: The objectives of this lesson are to: 1. Define refrigeration and air conditioning (Section 1.1) 2. Introduce aspects of various natural refrigeration methods, namely: a. Use of ice transported from colder regions (Section 1.2) b. Use of ice harvested in winter and stored in ice houses (Section 1.2) c. Use of ice produced by nocturnal cooling (Section 1.2.1) d. Use of evaporative cooling (Section 1.2.2) e. Cooling by salt solutions (Section 1.2.3) 3. Introduce historical aspects of various artificial refrigeration methods, namely: a. Vapour compression refrigeration systems, including i. Domestic refrigeration systems (Section 1.3.1.1) ii. Air conditioning systems (Section 1.3.1.2) b. Vapour absorption refrigeration systems (Section 1.3.2) c. Solar energy based refrigeration systems (Section 1.3.3) d. Air cycle refrigeration systems (Section 1.3.4) e. Steam and vapor jet refrigeration systems (Section 1.3.5) f. Thermoelectric refrigeration systems (Section 1.3.6), and g. Vortex tubes (Section 1.3.7) At the end of the lesson the student should be able to: 1. Identify various natural and artificial methods of refrigeration 2. List salient points of various refrigeration techniques, and 3. Name important landmarks in the history of refrigeration 1.1. Introduction Refrigeration may be defined as the process of achieving and maintaining a temperature below that of the surroundings, the aim being to cool some product or space to the required temperature. One of the most important applications of refrigeration has been the preservation of perishable food products by storing them at low temperatures. Refrigeration systems are also used extensively for providing thermal comfort to human beings by means of air conditioning. Air Conditioning refers to the treatment of air so as to simultaneously control its temperature, moisture content, cleanliness, odour and circulation, as required by occupants, a process, or products in the space. The subject of refrigeration and air conditioning has evolved out of human need for food and comfort, and its history dates back to centuries. The history of refrigeration is very interesting since every aspect of it, the availability of refrigerants, the prime movers and the developments in compressors and the methods of refrigeration all are a part of it. The French scientist Roger ThÝvenot has written an excellent book on the history of refrigeration throughout the world. Here we present only a 2 Version 1 ME, IIT Kharagpur
  • 9. brief history of the subject with special mention of the pioneers in the field and some important events. Q: Which of the following can be called as a refrigeration process? a) Cooling of hot ingot from 1000oC to room temperature b) Cooling of a pot of water by mixing it with a large block of ice c) Cooling of human beings using a ceiling fan d) Cooling of a hot cup of coffee by leaving it on a table e) Cooling of hot water by mixing it with tap water f) Cooling of water by creating vacuum over it Ans: b) and f) 1.2. Natural Refrigeration In olden days refrigeration was achieved by natural means such as the use of ice or evaporative cooling. In earlier times, ice was either: 1. Transported from colder regions, 2. Harvested in winter and stored in ice houses for summer use or, 3. Made during night by cooling of water by radiation to stratosphere. In Europe, America and Iran a number of icehouses were built to store ice. Materials like sawdust or wood shavings were used as insulating materials in these icehouses. Later on, cork was used as insulating material. Literature reveals that ice has always been available to aristocracy who could afford it. In India, the Mogul emperors were very fond of ice during the harsh summer in Delhi and Agra, and it appears that the ice used to be made by nocturnal cooling. In 1806, Frederic Tudor, (who was later called as the “ice king”) began the trade in ice by cutting it from the Hudson River and ponds of Massachusetts and exporting it to various countries including India. In India Tudor’s ice was cheaper than the locally manufactured ice by nocturnal cooling. The ice trade in North America was a flourishing business. Ice was transported to southern states of America in train compartments insulated by 0.3m of cork insulation. Trading in ice was also popular in several other countries such as Great Britain, Russia, Canada, Norway and France. In these countries ice was either transported from colder regions or was harvested in winter and stored in icehouses for use in summer. The ice trade reached its peak in 1872 when America alone exported 225000 tonnes of ice to various countries as far as China and Australia. However, with the advent of artificial refrigeration the ice trade gradually declined. 1.2.1. Art of Ice making by Nocturnal Cooling: The art of making ice by nocturnal cooling was perfected in India. In this method ice was made by keeping a thin layer of water in a shallow earthen tray, and then exposing the tray to the night sky. Compacted hay of about 0.3 m thickness was used as insulation. The water looses heat by radiation to the stratosphere, which is at around -55˚C and by early morning hours the water in the trays freezes to ice. This method of ice production was very popular in India. 3 Version 1 ME, IIT Kharagpur
  • 10. 1.2.2. Evaporative Cooling: As the name indicates, evaporative cooling is the process of reducing the temperature of a system by evaporation of water. Human beings perspire and dissipate their metabolic heat by evaporative cooling if the ambient temperature is more than skin temperature. Animals such as the hippopotamus and buffalo coat themselves with mud for evaporative cooling. Evaporative cooling has been used in India for centuries to obtain cold water in summer by storing the water in earthen pots. The water permeates through the pores of earthen vessel to its outer surface where it evaporates to the surrounding, absorbing its latent heat in part from the vessel, which cools the water. It is said that Patliputra University situated on the bank of river Ganges used to induce the evaporative-cooled air from the river. Suitably located chimneys in the rooms augmented the upward flow of warm air, which was replaced by cool air. Evaporative cooling by placing wet straw mats on the windows is also very common in India. The straw mat made from “khus” adds its inherent perfume also to the air. Now-a-days desert coolers are being used in hot and dry areas to provide cooling in summer. 1.2.3. Cooling by Salt Solutions: Certain substances such as common salt, when added to water dissolve in water and absorb its heat of solution from water (endothermic process). This reduces the temperature of the solution (water+salt). Sodium Chloride salt (NaCl) can yield temperatures up to -20˚C and Calcium Chloride (CaCl2) up to - 50˚C in properly insulated containers. However, as it is this process has limited application, as the dissolved salt has to be recovered from its solution by heating. Q. The disadvantages of natural refrigeration methods are: a) They are expensive b) They are uncertain c) They are not environment friendly d) They are dependent on local conditions Ans: b) and d) Q. Evaporative cooling systems are ideal for: a) Hot and dry conditions b) Hot and humid conditions c) Cold and humid conditions d) Moderately hot but humid conditions Ans: a) 4 Version 1 ME, IIT Kharagpur
  • 11. 1.3. Artificial Refrigeration Refrigeration as it is known these days is produced by artificial means. Though it is very difficult to make a clear demarcation between natural and artificial refrigeration, it is generally agreed that the history of artificial refrigeration began in the year 1755, when the Scottish professor William Cullen made the first refrigerating machine, which could produce a small quantity of ice in the laboratory. Based on the working principle, refrigeration systems can be classified as vapour compression systems, vapour absorption systems, gas cycle systems etc. 1.3.1. Vapour Compression Refrigeration Systems: The basis of modern refrigeration is the ability of liquids to absorb enormous quantities of heat as they boil and evaporate. Professor William Cullen of the University of Edinburgh demonstrated this in 1755 by placing some water in thermal contact with ether under a receiver of a vacuum pump. The evaporation rate of ether increased due to the vacuum pump and water could be frozen. This process involves two thermodynamic concepts, the vapour pressure and the latent heat. A liquid is in thermal equilibrium with its own vapor at a pressure called the saturation pressure, which depends on the temperature alone. If the pressure is increased for example in a pressure cooker, the water boils at higher temperature. The second concept is that the evaporation of liquid requires latent heat during evaporation. If latent heat is extracted from the liquid, the liquid gets cooled. The temperature of ether will remain constant as long as the vacuum pump maintains a pressure equal to saturation pressure at the desired temperature. This requires the removal of all the vapors formed due to vaporization. If a lower temperature is desired, then a lower saturation pressure will have to be maintained by the vacuum pump. The component of the modern day refrigeration system where cooling is produced by this method is called evaporator. If this process of cooling is to be made continuous the vapors have to be recycled by condensation to the liquid state. The condensation process requires heat rejection to the surroundings. It can be condensed at atmospheric temperature by increasing its pressure. The process of condensation was learned in the second half of eighteenth century. U.F. Clouet and G. Monge liquefied SO2 in 1780 while van Marum and Van Troostwijk liquefied NH3 in 1787. Hence, a compressor is required to maintain a high pressure so that the evaporating vapours can condense at a temperature greater than that of the surroundings. Oliver Evans in his book “Abortion of a young Steam Engineer’s Guide” published in Philadelphia in 1805 described a closed refrigeration cycle to produce ice by ether under vacuum. Jacob Perkins, an American living in London actually designed such a system in1835. The apparatus described by Jacob Perkins in his patent specifications of 1834 is shown in Fig.1.1. In his patent he stated “I am enabled to use volatile fluids for the purpose of producing the cooling or freezing of fluids, and yet at the same time constantly condensing such volatile fluids, and bringing them again into operation without waste”. 5 Version 1 ME, IIT Kharagpur
  • 12. Fig. 1.1. Apparatus described by Jacob Perkins in his patent specification of 1834. The refrigerant (ether or other volatile fluid) boils in evaporator B taking heat from surrounding water in container A. The pump C draws vapour away and compresses it to higher pressure at which it can condense to liquids in tubes D, giving out heat to water in vessel E. Condensed liquid flows through the weight loaded valve H, which maintains the difference of pressure between the condenser and evaporator. The small pump above H is used for charging the apparatus with refrigerant. John Hague made Perkins’s design into working model with some modifications. This Perkins machine is shown in Fig.1.2. The earliest vapour compression system used either sulphuric (ethyl) or methyl ether. The American engineer Alexander Twining (1801-1884) received a British patent in 1850 for a vapour compression system by use of ether, NH3 and CO2. The man responsible for making a practical vapor compression refrigeration system was James Harrison who took a patent in 1856 for a vapour compression system using ether, alcohol or ammonia. Charles Tellier of France patented in 1864, a refrigeration system using dimethyl ether which has a normal boiling point of −23.6˚C. 6 Version 1 ME, IIT Kharagpur
  • 13. Fig.1.2. Perkins machine built by John Hague Carl von Linde in Munich introduced double acting ammonia compressor. It required pressures of more than 10 atmospheres in the condenser. Since the normal boiling point of ammonia is -33.3˚C, vacuum was not required on the low pressure side. Since then ammonia is used widely in large refrigeration plants. David Boyle, in fact made the first NH3 system in 1871 in San Francisco. John Enright had also developed a similar system in 1876 in Buffalo N.Y. Franz Windhausen developed carbon dioxide (CO2) based vapor compression system in Germany in 1886. The carbon dioxide compressor requires a pressure of about 80 atmospheres and therefore a very heavy construction. Linde in 1882 and T.S.C. Lowe in 1887 tried similar systems in USA. The CO2 system is a very safe system and was used in ship refrigeration until 1960s. Raoul Pictet used SO2 (NBP -10˚C) as refrigerant. Its lowest pressure was high enough to prevent the leakage of air into the system. Palmer used C2H5Cl in 1890 in a rotary compressor. He mixed it with C2H5Br to reduce its flammability. Edmund Copeland and Harry Edwards used iso-butane in 1920 in small refrigerators. It disappeared by 1930 when it was replaced by CH3Cl. Dichloroethylene (Dielene or Dieline) was used by Carrier in centrifugal compressors in 1922-26. 1.3.1.1. Domestic refrigeration systems: The domestic refrigerator using natural ice (domestic ice box) was invented in 1803 and was used for almost 150 years without much alteration. The domestic ice box used to be made of wood with suitable insulation. Ice used to be kept at the top of the box, and low temperatures are produced in the box due to heat transfer from ice by natural convection. A drip pan is used to collect the water formed due to the melting of ice. The box has to be replenished with fresh ice once all the ice melts. Though the concept is quite simple, the domestic ice box suffered from several disadvantages. The user has to replenish the ice as 7 Version 1 ME, IIT Kharagpur
  • 14. soon as it is consumed, and the lowest temperatures that could be produced inside the compartment are limited. In addition, it appears that warm winters caused severe shortage of natural ice in USA. Hence, efforts, starting from 1887 have been made to develop domestic refrigerators using mechanical systems. The initial domestic mechanical refrigerators were costly, not completely automatic and were not very reliable. However, the development of mechanical household refrigerators on a large scale was made possible by the development of small compressors, automatic refrigerant controls, better shaft seals, developments in electrical power systems and induction motors. General Electric Company introduced the first domestic refrigerator in 1911, followed by Frigidaire in 1915. Kelvinator launched the domestic mechanical refrigerator in 1918 in USA. In 1925, USA had about 25 million domestic refrigerators of which only 75000 were mechanical. However, the manufacture of domestic refrigerators grew very rapidly, and by 1949 about 7 million domestic refrigerators were produced annually. With the production volumes increasing the price fell sharply (the price was 600 dollars in 1920 and 155 dollars in 1940). The initial domestic refrigerators used mainly sulphur dioxide as refrigerant. Some units used methyl chloride and methylene chloride. These refrigerants were replaced by Freon-12 in 1930s. In the beginning these refrigerators were equipped with open type compressors driven by belt drive. General Electric Company introduced the first refrigerator with a hermetic compressor in 1926. Soon the open type compressors were completely replaced by the hermetic compressors. First refrigerators used water-cooled condensers, which were soon replaced by air cooled- condensers. Though the development of mechanical domestic refrigerators was very rapid in USA, it was still rarely used in other countries. In 1930 only rich families used domestic refrigerators in Europe. The domestic refrigerator based on absorption principle as proposed by Platen and Munters, was first made by Electrolux Company in 1931 in Sweden. In Japan the first mechanical domestic refrigerator was made in 1924. The first dual temperature (freezer-refrigerator) domestic refrigerator was introduced in 1939. The use of mechanical domestic refrigerators grew rapidly all over the world after the Second World War. Today, a domestic refrigerator has become an essential kitchen appliance not only in highly developed countries but also in countries such as India. Except very few almost all the present day domestic refrigerators are mechanical refrigerators that use a hermetic compressor and an air cooled condenser. The modern refrigerators use either HFC-134a (hydro-fluoro-carbon) or iso-butane as refrigerant. 1.3.1.2. Air conditioning systems: Refrigeration systems are also used for providing cooling and dehumidification in summer for personal comfort (air conditioning). The first air conditioning systems were used for industrial as well as comfort air conditioning. Eastman Kodak installed the first air conditioning system in 1891 in Rochester, New York for the storage of photographic films. An air conditioning system was installed in a printing press in 1902 and in a telephone exchange in Hamburg in 1904. Many systems were installed in tobacco and textile factories around 1900. The first domestic air conditioning system was installed in a house in Frankfurt in 1894. A private library in St Louis, USA was air conditioned in 1895, and a casino was air conditioned in Monte Carlo in 1901. Efforts have also been made to air condition passenger rail coaches using ice. The widespread development of air conditioning is attributed to the American scientist and industrialist Willis Carrier. Carrier studied the control of humidity in 1902 and designed a central air conditioning plant using air washer in 1904. Due to the pioneering efforts of Carrier and also due to simultaneous development of different components and controls, air conditioning quickly became very popular, especially after 1923. At present comfort air conditioning is widely used in residences, offices, commercial buildings, air ports, hospitals and in mobile applications such as rail coaches, automobiles, 8 Version 1 ME, IIT Kharagpur
  • 15. aircrafts etc. Industrial air conditioning is largely responsible for the growth of modern electronic, pharmaceutical, chemical industries etc. Most of the present day air conditioning systems use either a vapour compression refrigeration system or a vapour absorption refrigeration system. The capacities vary from few kilowatts to megawatts. Figure 1.3 shows the basic components of a vapour compression refrigeration system. As shown in the figure the basic system consists of an evaporator, compressor, condenser and an expansion valve. The refrigeration effect is obtained in the cold region as heat is extracted by the vaporization of refrigerant in the evaporator. The refrigerant vapour from the evaporator is compressed in the compressor to a high pressure at which its saturation temperature is greater than the ambient or any other heat sink. Hence when the high pressure, high temperature refrigerant flows through the condenser, condensation of the vapour into liquid takes place by heat rejection to the heat sink. To complete the cycle, the high pressure liquid is made to flow through an expansion valve. In the expansion valve the pressure and temperature of the refrigerant decrease. This low pressure and low temperature refrigerant vapour evaporates in the evaporator taking heat from the cold region. It should be observed that the system operates on a closed cycle. The system requires input in the form of mechanical work. It extracts heat from a cold space and rejects heat to a high temperature heat sink. Fig.1.3. Schematic of a basic vapour compression refrigeration system A refrigeration system can also be used as a heat pump, in which the useful output is the high temperature heat rejected at the condenser. Alternatively, a refrigeration system can be used for providing cooling in summer and heating in winter. Such systems have been built and are available now. 9 Version 1 ME, IIT Kharagpur
  • 16. Q. Compared to natural refrigeration methods, artificial refrigeration methods are: a) Continuous b) Reliable c) Environment friendly d) Can work under almost all conditions Ans. a), b) and d) Q. In the evaporator of a vapour compression refrigeration system: a) A low temperature is maintained so that heat can flow from the external fluid b) Refrigeration effect is produced as the refrigerant liquid vaporizes c) A low pressure is maintained so that the compressor can run d) All of the above Ans. a) and b) Q. The function of a compressor in a vapour compression refrigeration system is to: a) To maintain the required low-side pressure in the evaporator b) To maintain the required high-side pressure in the condenser c) To circulate required amount of refrigerant through the system d) To safeguard the refrigeration system Ans. a), b) and c) Q. In a vapour compression refrigeration system, a condenser is primarily required so that: a) A high pressure can be maintained in the system b) The refrigerant evaporated in the evaporator can be recycled c) Performance of the system can be improved d) Low temperatures can be produced Ans. b) Q. The function of an expansion valve is to: a) Reduce the refrigerant pressure b) Maintain high and low side pressures c) Protect evaporator d) All of the above Ans. b) Q. In a domestic icebox type refrigerator, the ice block is kept at the top because: a) It is convenient to the user b) Disposal of water is easier c) Cold air can flow down due to buoyancy effect d) None of the above Ans. c) Q. An air conditioning system employs a refrigeration system to: a) Cool and dehumidify air supplied to the conditioned space b) To heat and humidify the air supplied to the conditioned space c) To circulate the air through the system d) To purify the supply air Ans. a) 10 Version 1 ME, IIT Kharagpur
  • 17. 1.3.2. Vapour Absorption Refrigeration Systems: John Leslie in 1810 kept H2SO4 and water in two separate jars connected together. H2SO4 has very high affinity for water. It absorbs water vapour and this becomes the principle of removing the evaporated water vapour requiring no compressor or pump. H2SO4 is an absorbent in this system that has to be recycled by heating to get rid of the absorbed water vapour, for continuous operation. Windhausen in 1878 used this principle for absorption refrigeration system, which worked on H2SO4. Ferdinand Carre invented aqua- ammonia absorption system in 1860. Water is a strong absorbent of NH3. If NH3 is kept in a vessel that is exposed to another vessel containing water, the strong absorption potential of water will cause evaporation of NH3 requiring no compressor to drive the vapours. A liquid pump is used to increase the pressure of strong solution. The strong solution is then heated in a generator and passed through a rectification column to separate the water from ammonia. The ammonia vapour is then condensed and recycled. The pump power is negligible hence; the system runs virtually on low- grade energy used for heating the strong solution to separate the water from ammonia. These systems were initially run on steam. Later on oil and natural gas based systems were introduced. Figure 1.4 shows the essential components of a vapour absorption refrigeration system. In 1922, Balzar von Platen and Carl Munters, two students at Royal Institute of Technology, Stockholm invented a three fluid system that did not require a pump. A heating based bubble pump was used for circulation of strong and weak solutions and hydrogen was used as a non-condensable gas to reduce the partial pressure of NH3 in the evaporator. Geppert in 1899 gave this original idea but he was not successful since he was using air as non-condensable gas. The Platen-Munters refrigeration systems are still widely used in certain niche applications such as hotel rooms etc. Figure 1.5 shows the schematic of the triple fluid vapour absorption refrigeration system. Fig.1.4. Essential components of a vapour absorption refrigeration system 11 Version 1 ME, IIT Kharagpur
  • 18. Fig.1.5. Schematic of a triple fluid vapour absorption refrigeration system Another variation of vapour absorption system is the one based on Lithium Bromide (LiBr)-water. This system is used for chilled water air-conditioning system. This is a descendent of Windhausen’s machine with LiBr replacing H2SO4. In this system LiBr is the absorbent and water is the refrigerant. This system works at vacuum pressures. The condenser and the generator are housed in one cylindrical vessel and the evaporator and the absorber are housed in second vessel. This also runs on low-grade energy requiring a boiler or process steam. 1.3.3. Solar energy based refrigeration systems: Attempts have been made to run vapour absorption systems by solar energy with concentrating and flat plate solar collectors. Several small solar absorption refrigeration systems have been made around 1950s in several countries. Professor G.O.G. L f of America is one of the pioneers in the area of solar refrigeration using flat plate collectors. A solar refrigeration system that could produce 250 kg of ice per day was installed in Tashkent, USSR in 1953. This system used a parabolic mirror of 10 m2 area for concentrating the solar radiation. F. Trombe installed an absorption machine with a cylindro-parabolic mirror of 20 m2 at Montlouis, France, which produced 100 kg of ice per day. Serious consideration to solar refrigeration systems was given since 1965, due to the scarcity of fossil fuel based energy sources. LiBr-water based systems have been developed for air conditioning purposes. The first solar air conditioning system was installed in an experimental solar house in University of Queensland, Australia in 1966. After this several systems based on solar energy were built in many parts of the world including India. In 1976, there were about 500 solar absorption systems in USA alone. Almost all these were based on LiBr-water as these systems do not require very high heating temperatures. These systems were mainly used for space air conditioning. Intermittent absorption systems based on solar energy have also been built and operated successfully. In these systems, the cooling effect is obtained during the nighttime, while the system gets “charged” during the day using solar energy. Though the efficiency of these systems is rather poor requiring solar collector area, they may find applications in 12 Version 1 ME, IIT Kharagpur
  • 19. remote and rural areas where space is not a constraint. In addition, these systems are environment friendly as they use eco-friendly refrigerants and run on clean and renewable solar energy. Solar adsorption refrigeration system with ammoniacates, sodium thiocyanate, activated charcoal, zeolite as adsorbents and ammonia, alcohols or fluorocarbons as refrigerants have also been in use since 1950s. These systems also do not require a compressor. The refrigerant vapour is driven by the adsorption potential of the adsorbent stored in an adsorbent bed. This bed is connected to an evaporator/condenser, which consists of the pure refrigerant. In intermittent adsorption systems, during the night the refrigerant evaporates and is adsorbed in activated charcoal or zeolite providing cooling effect. During daytime the adsorbent bed absorbs solar radiation and drives off the refrigerant stored in the bed. This refrigerant vapour condenses in the condenser and stored in a reservoir for nighttime use. Thus this simple system consists of an adsorbent bed and a heat exchanger, which acts as a condenser during the nighttime and, as an evaporator during the night. Pairs of such reactors can be used for obtaining a continuous cooling Q. Compared to the compression systems, vapour absorption refrigeration systems: a) Are environment friendly b) Use low-grade thermal energy for operation c) Cannot be used for large capacity refrigeration systems d) Cannot be used for small capacity refrigeration systems Ans. a) and b) Q. In absorption refrigeration systems, the compressor of vapour compression systems is replaced by: a) Absorber b) Generator c) Pump d) All of the above Ans. d) Q. In a triple fluid vapour absorption refrigeration system, the hydrogen gas is used to: a) Improve system performance b) Reduce the partial pressure of refrigerant in evaporator c) Circulate the refrigerant d) Provide a vapour seal Ans. b) Q. Solar energy based refrigeration systems are developed to: a) Reduce fossil fuel consumption b) Provide refrigeration in remote areas c) Produce extremely low temperatures d) Eliminate compressors Ans. a) and b) Q. Solar energy based refrigeration systems: a) Cannot be used for large capacity systems b) Cannot be made continuous c) Are not environment friendly d) None of the above Ans. d) 13 Version 1 ME, IIT Kharagpur
  • 20. 1.3.4. Gas Cycle Refrigeration: If air at high pressure expands and does work (say moves a piston or rotates a turbine), its temperature will decrease. This fact is known to man as early as the 18th century. Dalton and Gay Lusaac studied this in 1807. Sadi Carnot mentioned this as a well-known phenomenon in 1824. However, Dr. John Gorrie a physician in Florida developed one such machine in 1844 to produce ice for the relief of his patients suffering from fever. This machine used compressed air at 2 atm. pressure and produced brine at a temperature of –7oC, which was then used to produce ice. Alexander Carnegie Kirk in 1862 made an air cycle cooling machine. This system used steam engine to run its compressor. Using a compression ratio of 6 to 8, Kirk could produce temperatures as low as 40oC. Paul Gifford in 1875 perfected the open type of machine. This machine was further improved by T B Lightfoot, A Haslam, Henry Bell and James Coleman. This was the main method of marine refrigeration for quite some time. Frank Allen in New York developed a closed cycle machine employing high pressures to reduce the volume flow rates. This was named dense air machine. These days air cycle refrigeration is used only in aircrafts whose turbo compressor can handle large volume flow rates. Figure 1.6 shows the schematic of an open type air cycle refrigeration system. The basic system shown here consists of a compressor, an expander and a heat exchanger. Air from the cold room is compressed in the compressor. The hot and high pressure air rejects heat to the heat sink (cooling water) in the heat exchanger. The warm but high pressure air expands in the expander. The cold air after expansion is sent to the cold room for providing cooling. The work of expansion partly compensates the work of compression; hence both the expander and the compressor are mounted on a common shaft. Fig.1.6. Schematic of a basic, open type air cycle refrigeration system 14 Version 1 ME, IIT Kharagpur
  • 21. 1.3.5. Steam Jet Refrigeration System: If water is sprayed into a chamber where a low pressure is maintained, a part of the water will evaporate. The enthalpy of evaporation will cool the remaining water to its saturation temperature at the pressure in the chamber. Obviously lower temperature will require lower pressure. Water freezes at 0oC hence temperature lower than 4oC cannot be obtained with water. In this system, high velocity steam is used to entrain the evaporating water vapour. High-pressure motive steam passes through either convergent or convergent- divergent nozzle where it acquires either sonic or supersonic velocity and low pressure of the order of 0.009 kPa corresponding to an evaporator temperature of 4oC. The high momentum of motive steam entrains or carries along with it the water vapour evaporating from the flash chamber. Because of its high velocity it moves the vapours against the pressure gradient up to the condenser where the pressure is 5.6-7.4 kPa corresponding to condenser temperature of 35-45oC. The motive vapour and the evaporated vapour both are condensed and recycled. This system is known as steam jet refrigeration system. Figure 1.7 shows a schematic of the system. It can be seen that this system requires a good vacuum to be maintained. Sometimes, booster ejector is used for this purpose. This system is driven by low- grade energy that is process steam in chemical plants or a boiler. Fig.1.7. Schematic of a steam jet refrigeration system In 1838, the Frenchman Pelletan was granted a patent for the compression of steam by means of a jet of motive steam. Around 1900, the Englishman Charles Parsons studied the possibility of reduction of pressure by an entrainment effect from a steam jet. However, the credit for constructing the steam jet refrigeration system goes to the French engineer, Maurice Leblanc who developed the system in 1907-08. In this system, ejectors were used to produce a high velocity steam jet (≈ 1200 m/s). Based on Leblanc’s design the first commercial system was made by Westinghouse in 1909 in Paris. Even though the efficiency of the steam jet refrigeration system was low, it was still attractive as water is harmless and the system can run using exhaust steam from a steam engine. From 1910 onwards, stem jet refrigeration 15 Version 1 ME, IIT Kharagpur
  • 22. systems were used mainly in breweries, chemical factories, warships etc. In 1926, the French engineer Follain improved the machine by introducing multiple stages of vaporization and condensation of the suction steam. Between 1928-1930, there was much interest in this type of systems in USA. In USA they were mainly used for air conditioning of factories, cinema theatres, ships and even railway wagons. Several companies such as Westinghouse, Ingersoll Rand and Carrier started commercial production of these systems from 1930. However, gradually these systems were replaced by more efficient vapour absorption systems using LiBr-water. Still, some east European countries such as Czechoslovakia and Russia manufactured these systems as late as 1960s. The ejector principle can also be used to provide refrigeration using fluids other than water, i.e., refrigerants such as CFC-11, CFC-21, CFC-22, CFC-113, CFC-114 etc. The credit for first developing these closed vapour jet refrigeration systems goes to the Russian engineer, I.S. Badylkes around 1955. Using refrigerants other than water, it is possible to achieve temperatures as low as –100oC with a single stage of compression. The advantages cited for this type of systems are simplicity and robustness, while difficult design and economics are its chief disadvantages. 1.3.6. Thermoelectric Refrigeration Systems: In 1821 the German physicist T.J. Seebeck reported that when two junctions of dissimilar metals are kept at two different temperatures, an electro motive force (emf) is developed, resulting in flow of electric current. The emf produced is found to be proportional to temperature difference. In 1834, a Frenchmen, J. Peltier observed the reverse effect, i.e., cooling and heating of two junctions of dissimilar materials when direct current is passed through them, the heat transfer rate being proportional to the current. In 1838, H.F.E. Lenz froze a drop of water by the Peltier effect using antimony and bismuth (it was later found that Lenz could freeze water as the materials used were not pure metals but had some impurities in them). In 1857, William Thomson (Lord Kelvin) proved by thermodynamic analysis that Seebeck effect and Peltier effect are related and he discovered another effect called Thomson effect after his name. According to this when current flows through a conductor of a thermocouple that has an initial temperature gradient in it, then heat transfer rate per unit length is proportional to the product of current and the temperature. As the current flow through thermoelectric material it gets heated due to its electrical resistance. This is called the Joulean effect, further, conduction heat transfer from the hot junction to the cold junction transfers heat. Both these heat transfer rates have to be compensated by the Peltier Effect for some useful cooling to be produced. For a long time, thermoelectric cooling based on the Peltier effect remained a laboratory curiosity as the temperature difference that could be obtained using pure metals was too small to be of any practical use. Insulating materials give poor thermoelectric performance because of their small electrical conductivity while metals are not good because of their large thermal conductivity. However, with the discovery of semiconductor materials in 1949-50, the available temperature drop could be increased considerably, giving rise to commercialization of thermoelectric refrigeration systems. Figure 1.8 shows the schematic of the thermoelectric refrigeration system based on semiconductor materials. The Russian scientist, A. F. Ioffe is one of the pioneers in the area of thermoelectric refrigeration systems using semiconductors. Several domestic refrigerators based on thermoelectric effect were made in USSR as early as 1949. However, since 1960s these systems are used mainly used for storing medicines, vaccines etc and in electronic cooling. Development also took place in many other countries. In USA domestic refrigerators, air conditioners, water coolers, air conditioned diving suits etc. were made 16 Version 1 ME, IIT Kharagpur
  • 23. 12V Fig. 1.8. Schematic of a thermoelectric refrigeration system using these effects. System capacities were typically small due to poor efficiency. However some large refrigeration capacity systems such as a 3000 kcal/h air conditioner and a 6 tonne capacity cold storage were also developed. By using multistaging temperatures as low as – 145oC were obtained. These systems due to their limited performance (limited by the materials) are now used only in certain niche applications such as electronic cooling, mobile coolers etc. Efforts have also been made to club thermoelectric systems with photovoltaic cells with a view to develop solar thermoelectric refrigerators. 1.3.7. Vortex tube systems: In 1931, the French engineer Georges Ranque (1898-1973) discovered an interesting phenomenon, which is called “Ranque effect” or “vortex effect”. The tangential injection of air into a cylindrical tube induces to quote his words “ a giratory expansion with simultaneous production of an escape of hot air and an escape of cold air”. Ranque was granted a French patent in 1928 and a US patent in 1934 for this effect. However, the discovery was neglected until after the second world war, when in 1945, Rudolph Hilsch, a German physicist, studied this effect and published a widely read scientific paper on this device. Thus, the vortex tube has also been known as the "Ranque-Hilsch Tube”. Though the efficiency of this system is quite low, it is very interesting due to its mechanical simplicity and instant cooling. It is convenient where there is a supply of compressed air. The present day vortex tube uses compressed air as a power source, it has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of these two airstreams are adjustable with a valve built into the hot air exhaust. Temperatures as low as −46°C and as high as 127°C are possible. Compressed air is supplied to the vortex tube and passes through nozzles that are tangential to an internal counter bore. These nozzles set the air in a vortex motion. This spinning stream of air turns 90° and passes down the hot tube in the form of a spinning shell, similar to a tornado. A valve at one end of the tube allows some of the warmed air to escape. What does not escape, heads back down the tube as a second vortex inside the low-pressure area of the larger vortex. This inner vortex loses heat and exhausts through the other end as cold air. Currently vortex tube is used for spot cooling of machine parts, in electronic cooling and also in cooling jackets for miners, firemen etc. 17 Version 1 ME, IIT Kharagpur
  • 24. Q. In an air cycle refrigeration system, low temperatures are produced due to: a) Evaporation of liquid air b) Throttling of air c) Expansion of air in turbine d) None of the above Ans. c) Q. Air cycle refrigeration systems are most commonly used in: a) Domestic refrigerators b) Aircraft air conditioning systems c) Cold storages d) Car air conditioning systems Ans. b) Q. The required input to the steam jet refrigeration systems is in the form of: a) Mechanical energy b) Thermal energy c) High pressure, motive steam d) Both mechanical and thermal energy Ans. c) Q. A nozzle is used in steam jet refrigeration systems to: a) To convert the high pressure motive steam into high velocity steam b) To reduce energy consumption c) To improve safety aspects d) All of the above Ans. a) Q. The materials used in thermoelectric refrigeration systems should have: a) High electrical and thermal conductivity b) High electrical conductivity and low thermal conductivity c) Low electrical conductivity and high thermal conductivity c) Low electrical and thermal conductivity Ans. b) Q. A thermoelectric refrigeration systems requires: a) A high voltage AC (alternating current) input b) A low voltage AC input c) A high voltage DC (direct current) input d) A low voltage DC input Ans. d). 18 Version 1 ME, IIT Kharagpur
  • 25. 1.3.8. Summary: In this lecture the student is introduced to different methods of refrigeration, both natural and artificial. Then a brief history of artificial refrigeration techniques is presented with a mention of the pioneers in this field and important events. The working principles of these systems are also described briefly. In subsequent chapters the most important of these refrigeration systems will be discussed in detail. Questions: Q. Explain why ice making using nocturnal cooling is difficult on nights when the sky is cloudy? Ans. In order to make ice from water, water has to be first sensibly cooled from its initial temperature to its freezing point (0oC) and then latent heat has to be transferred at 0oC. This requires a heat sink that is at a temperature lower than 0oC. Ice making using nocturnal cooling relies on radiative heat transfer from the water to the sky (which is at about 55oC) that acts as a heat sink. When the sky is cloudy, the clouds reflect most of the radiation back to earth and the effective surface temperature of clouds is also much higher. As a result, radiative heat transfer from the water becomes very small, making the ice formation difficult. Q. When you add sufficient amount of glucose to a glass of water, the water becomes cold. Is it an example of refrigeration, if it is, can this method be used for devising a refrigeration system? Ans. Yes, this is an example of refrigeration as the temperature of glucose solution is lower than the surroundings. However, this method is not viable, as the production of refrigeration continuously requires an infinite amount of water and glucose or continuous recovery of glucose from water. Q. To what do you attribute the rapid growth of refrigeration technology over the last century? Ans. The rapid growth of refrigeration technology over the last century can be attributed to several reasons, some of them are: i. Growing global population leading to growing demand for food, hence, demand for better food processing and food preservation methods. Refrigeration is required for both food processing and food preservation (Food Chain) ii. Growing demand for refrigeration in almost all industries iii. Growing demand for comfortable conditions (air conditioned) at residences, workplaces etc. iv. Rapid growth of technologies required for manufacturing various refrigeration components v. Availability of electricity, and vi. Growing living standards 19 Version 1 ME, IIT Kharagpur
  • 26. Lesson 2 History Of Refrigeration – Development Of Refrigerants And Compressors 1 Version 1 ME, IIT Kharagpur
  • 27. The objectives of the present lesson are to introduce the student to the history of refrigeration in terms of: 1. Refrigerant development (Section 2.2): i. Early refrigerants (Section 2.2.1) ii. Synthetic fluorocarbon based refrigerants (Section 2.2.2) iii. Non-ozone depleting refrigerants (Section 2.2.3) 2. Compressor development (Section 2.3): i. Low-speed steam engine driven compressors (Section 2.3.1) ii. High-speed electric motor driven compressors (Section 2.3.1) iii. Rotary vane and rolling piston compressors (Section 2.3.2) iv. Screw compressors (Section 2.3.2) v. Scroll compressors (Section 2.3.2) vi. Centrifugal compressors (Section 2.3.3) At the end of the lesson the student should be able to: i. State the importance of refrigerant selection ii. List various refrigerants used before the invention of CFCs iii. List various CFC refrigerants and their impact on refrigeration iv. State the environmental issues related to the use of CFCs v. State the refrigerant development after Montreal protocol vi. List important compressor types vii. List important landmarks in the development of compressors 2.1. Introduction: The development of refrigeration and air conditioning industry depended to a large extent on the development of refrigerants to suit various applications and the development of various system components. At present the industry is dominated by the vapour compression refrigeration systems, even though the vapour absorption systems have also been developed commercially. The success of vapour compression refrigeration systems owes a lot to the development of suitable refrigerants and compressors. The theoretical thermodynamic efficiency of a vapour compression system depends mainly on the operating temperatures. However, important practical issues such as the system design, size, initial and operating costs, safety, reliability, and serviceability etc. depend very much on the type of refrigerant and compressor selected for a given application. This lesson presents a brief history of refrigerants and compressors. The emphasis here is mainly on vapour compression refrigeration systems, as these are the most commonly used systems, and also refrigerants and compressors play a critical role here. The other popular type of refrigeration system, namely the vapour absorption type has seen fewer changes in terms of refrigerant development, and relatively less number of problems exist in these systems as far as the refrigerants are concerned. 2 Version 1 ME, IIT Kharagpur
  • 28. 2.2. Refrigerant development – a brief history In general a refrigerant may be defined as “any body or substance that acts as a cooling medium by extracting heat from another body or substance”. Under this general definition, many bodies or substances may be called as refrigerants, e.g. ice, cold water, cold air etc. In closed cycle vapour compression, absorption systems, air cycle refrigeration systems the refrigerant is a working fluid that undergoes cyclic changes. In a thermoelectric system the current carrying electrons may be treated as a refrigerant. However, normally by refrigerants we mean the working fluids that undergo condensation and evaporation as in compression and absorption systems. The history that we are talking about essentially refers to these substances. Since these substances have to evaporate and condense at required temperatures (which may broadly lie in the range of –100oC to +100oC) at reasonable pressures, they have to be essentially volatile. Hence, the development of refrigerants started with the search for suitable, volatile substances. Historically the development of these refrigerants can be divided into three distinct phases, namely: i. Refrigerants prior to the development of CFCs ii. The synthetic fluorocarbon (FC) based refrigerants iii. Refrigerants in the aftermath of stratospheric ozone layer depletion 2.2.1. Refrigerants prior to the development of CFCs Water is one of the earliest substances to be used as a refrigerant, albeit not in a closed system. Production of cold by evaporation of water dates back to 3000 B.C. Archaeological findings show pictures of Egyptian slaves waving fans in front of earthenware jars to accelerate the evaporation of water from the porous surfaces of the pots, thereby producing cold water. Of course, the use of “punkahs” for body cooling in hot summer is very well known in countries like India. Production of ice by nocturnal cooling is also well known. People also had some knowledge of producing sub-zero temperatures by the use of “refrigerant mixtures”. It is believed that as early as 4th Century AD people in India were using mixtures of salts (sodium nitrate, sodium chloride etc) and water to produce temperatures as low as –20oC. However, these natural refrigeration systems working with water have many limitations and hence were confined to a small number of applications. Water was the first refrigerant to be used in a continuous refrigeration system by William Cullen (1710-1790) in 1755. William Cullen is also the first man to have scientifically observed the production of low temperatures by evaporation of ethyl ether in 1748. Oliver Evans (1755-1819) proposed the use of a volatile fluid in a closed cycle to produce ice from water. He described a practical system that uses ethyl ether as the refrigerant. As already mentioned the credit for building the first vapour compression refrigeration system goes to Jakob Perkins (1766-1849). Perkins used sulphuric (ethyl) ether obtained from India rubber as refrigerant. Early commercial refrigerating machines developed by James Harrison (1816-1893) also used ethyl ether as refrigerant. Alexander Twining (1801-1884) also developed refrigerating machines using ethyl ether. After these developments, ethyl ether was used as refrigerant for several years for ice making, in breweries etc. Ether machines were gradually replaced by ammonia and carbon dioxide based machines, even though they were used for a longer time in tropical countries such as India. 3 Version 1 ME, IIT Kharagpur
  • 29. Ethyl ether appeared to be a good refrigerant in the beginning, as it was easier to handle it since it exists as a liquid at ordinary temperatures and atmospheric pressure. Ethyl ether has a normal boiling point (NBP) of 34.5oC, this indicates that in order to obtain low temperatures, the evaporator pressure must be lower than one atmosphere, i.e., operation in vacuum. Operation of a system in vacuum may lead to the danger of outside air leaking into the system resulting in the formation of a potentially explosive mixture. On the other hand a relatively high normal boiling point indicates lower pressures in the condenser, or for a given pressure the condenser can be operated at higher condensing temperatures. This is the reason behind the longer use of ether in tropical countries with high ambient temperatures. Eventually due to the high NBP, toxicity and flammability problems ethyl ether was replaced by other refrigerants. Charles Tellier (1828-1913) introduced dimethyl ether (NBP = 23.6oC) in 1864. However, this refrigerant did not become popular, as it is also toxic and inflammable. In 1866, the American T.S.C. Lowe (1832-1913) introduced carbon dioxide compressor. However, it enjoyed commercial success only in 1880s due largely to the efforts of German scientists Franz Windhausen (1829-1904) and Carl von Linde (1842-1934). Carbon dioxide has excellent thermodynamic and thermophysical properties, however, it has a low critical temperature (31.7oC) and very high operating pressures. Since it is non- flammable and non-toxic it found wide applications principally for marine refrigeration. It was also used for refrigeration applications on land. Carbon dioxide was used successfully for about sixty years however, it was completely replaced by CFCs. It is ironic to note that ever since the problem of ozone layer depletion was found, carbon dioxide is steadily making a comeback by replacing the synthetic CFCs/HCFCs/HFCs etc. One of the landmark events in the history of refrigerants is the introduction of ammonia. The American David Boyle (1837-1891) was granted the first patent for ammonia compressor in 1872. He made the first single acting vertical compressor in 1873. However, the credit for successfully commercializing ammonia systems goes to Carl von Linde (1842- 1934) of Germany, who introduced these compressors in Munich in 1876. Linde is credited with perfecting the ammonia refrigeration technology and owing to his pioneering efforts; ammonia has become one of the most important refrigerants to be developed. Ammonia has a NBP of 33.3oC, hence, the operating pressures are much higher than atmospheric. Ammonia has excellent thermodynamic and thermophysical properties. It is easily available and inexpensive. However, ammonia is toxic and has a strong smell and slight flammability. In addition, it is not compatible with some of the common materials of construction such as copper. Though these are considered to be some of its disadvantages, ammonia has stood the test of time and the onslaught of CFCs due to its excellent properties. At present ammonia is used in large refrigeration systems (both vapour compression and vapour absorption) and also in small absorption refrigerators (triple fluid vapour absorption). In 1874, Raoul Pictet (1846-1929) introduced sulphur dioxide (NBP= 10.0oC). Sulphur dioxide was an important refrigerant and was widely used in small refrigeration systems such as domestic refrigerators due to its small refrigerating effect. Sulphur dioxide has the advantage of being an auto-lubricant. In addition it is not only non-flammable, but actually acts as a flame extinguisher. However, in the presence of water vapour it produces sulphuric acid, which is highly corrosive. The problem of corrosion was overcome by an airtight sealed compressor (both motor and compressor are mounted in the same outer 4 Version 1 ME, IIT Kharagpur
  • 30. casing). However, after about sixty years of use in appliances such as domestic refrigerators, sulphur dioxide was replaced by CFCs. In addition to the above, other fluids such as methyl chloride, ethyl chloride, iso- butane, propane, ethyl alcohol, methyl and ethyl amines, carbon tetra chloride, methylene chloride, gasoline etc. were tried but discarded due to one reason or other. 2.2.2. The synthetic CFCs/HCFCs: Almost all the refrigerants used in the early stages of refrigeration suffered from one problem or other. Most of these problems were linked to safety issues such as toxicity, flammability, high operating pressures etc. As a result large-scale commercialization of refrigeration systems was hampered. Hence it was felt that “refrigeration industry needs a new refrigerant if they expect to get anywhere”. The task of finding a “safe” refrigerant was taken up by the American Thomas Midgley, Jr., in 1928. Midgley was already famous for the invention of tetra ethyl lead, an important anti-knock agent for petrol engines. Midgley along with his associates Albert L. Henne and Robert R. McNary at the Frigidaire Laboratories (Dayton, Ohio, USA) began a systematic study of the periodic table. From the periodic table they quickly eliminated all those substances yielding insufficient volatility. They then eliminated those elements resulting in unstable and toxic gases as well as the inert gases, based on their very low boiling points. They were finally left with eight elements: carbon, nitrogen, oxygen, sulphur, hydrogen, fluorine, chlorine and bromine. These eight elements clustered at an intersecting row and column of the periodic table, with fluorine at the intersection. Midgley and his colleagues then made three interesting observations: i. Flammability decreases from left to right for the eight elements ii. Toxicity generally decreases from the heavy elements at the bottom to the lighter elements at the top iii. Every known refrigerant at that time was made from the combination of those eight “Midgley” elements. A look at the refrigerants discussed above shows that all of them are made up of seven out of the eight elements identified by Midgley (fluorine was not used till then). Other researchers have repeated Midgley’s search with more modern search methods and databases, but arrived at the same conclusions (almost all the currently used refrigerants are made up of Midgley elements, only exception is Iodine, studies are being carried out on refrigerants containing iodine in addition to some of the Midgley elements). Based on their study, Midgely and his colleagues have developed a whole range of new refrigerants, which are obtained by partial replacement of hydrogen atoms in hydrocarbons by fluorine and chlorine. They have shown how fluorination and chlorination of hydrocarbons can be varied to obtain desired boiling points (volatility) and also how properties such as toxicity, flammability are influenced by the composition. The first commercial refrigerant to come out of Midgley’s study is Freon-12 in 1931. Freon-12 with a chemical formula CCl2F2, is obtained by replacing the four atoms of hydrogen in methane (CH4) by two atoms of chlorine and two atoms of fluorine. Freon-12 has a normal boiling point of 29.8oC, and is one of the most famous and popular synthetic refrigerants. It was exclusively used in small domestic refrigerators, air conditioners, water coolers etc for almost sixty years. Freon-11 (CCl3F) used in large centrifugal air conditioning systems was introduced in 1932. This is followed by Freon-22 (CHClF2) and a whole series of synthetic refrigerants to suit a wide variety of applications. 5 Version 1 ME, IIT Kharagpur
  • 31. Due to the emergence of a large number of refrigerants in addition to the existence of the older refrigerants, it has become essential to work out a numbering system for refrigerants. Thus all refrigerants were indicated with ‘R’ followed by a unique number (thus Freon-12 is changed to R12 etc). The numbering of refrigerants was done based on certain guidelines. For all synthetic refrigerants the number (e.g. 11, 12, 22) denotes the chemical composition. The number of all inorganic refrigerants begins with ‘7’ followed by their molecular weight. Thus R-717 denotes ammonia (ammonia is inorganic and its molecular weight is 17), R-718 denotes water etc.. Refrigerant mixtures begin with the number 4 (zeotropic) or 5 (azeotropic), e.g. R-500, R-502 etc. The introduction of CFCs and related compounds has revolutionized the field of refrigeration and air conditioning. Most of the problems associated with early refrigerants such as toxicity, flammability, and material incompatibility were eliminated completely. Also, Freons are highly stable compounds. In addition, by cleverly manipulating the composition a whole range of refrigerants best suited for a particular application could be obtained. In addition to all this, a vigorous promotion of these refrigerants as “wonder gases” and “ideal refrigerants” saw rapid growth of Freons and equally rapid exit of conventional refrigerants such as carbon dioxide, sulphur dioxide etc. Only ammonia among the older refrigerants survived the Freon magic. The Freons enjoyed complete domination for about fifty years, until the Ozone Layer Depletion issue was raised by Rowland and Molina in 1974. Rowland and Molina in their now famous theory argued that the highly stable chlorofluorocarbons cause the depletion of stratospheric ozone layer. Subsequent studies and observations confirmed Rowland and Molina theory on stratospheric ozone depletion by chlorine containing CFCs. In view of the seriousness of the problem on global scale, several countries have agreed to ban the harmful Ozone Depleting Substances, ODS (CFCs and others) in a phase-wise manner under Montreal Protocol. Subsequently almost all countries of the world have agreed to the plan of CFC phase-out. In addition to the ozone layer depletion, the CFCs and related substances were also found to contribute significantly to the problem of “global warming”. This once again brought the scientists back to the search for “safe” refrigerants. The “safety” now refers to not only the immediate personal safety issues such as flammability, toxicity etc., but also the long-term environmental issues such as ozone layer depletion and global warming. 2.2.3. Refrigerants in the aftermath of Ozone Layer Depletion: The most important requirement for refrigerants in the aftermath of ozone layer depletion is that it should be a non-Ozone Depleting Substance (non-ODS). Out of this requirement two alternatives have emerged. The first one is to look for zero ODP synthetic refrigerants and the second one is to look for “natural” substances. Introduction of hydrofluorocarbons (HFCs) and their mixtures belong to the first route, while the re- introduction of carbon dioxide (in a supercritical cycle), water and various hydrocarbons and their mixtures belong to the second route. The increased use of ammonia and use of other refrigeration cycles such as air cycle refrigeration systems and absorption systems also come under the second route. Both these routes have found their proponents and opponents. HFC- 134a (synthetic substance) and hydrocarbons (natural substances) have emerged as alternatives to Freon-12. No clear pure fluid alternative has been found as yet for the other popular refrigerant HCFC-22. However several mixtures consisting of synthetic and natural refrigerants are being used and suggested for future use. Table 2.1 shows the list of refrigerants being replaced and their alternatives. Mention must be made here about the other 6 Version 1 ME, IIT Kharagpur
  • 32. environmental problem, global warming. In general the non-ODS synthetic refrigerants such as HFC-134a have high global warming potential (GWP), hence they face an uncertain future. Since the global warming impact of a refrigerant also depends on the energy efficiency of the system using the refrigerant (indirect effect), the efficiency issue has become important in the design of new refrigeration systems. Though the issues of ozone layer depletion and global warming has led to several problems, they have also had beneficial effects of making people realize the importance of environmental friendliness of technologies. It is expected that with the greater awareness more responsible designs will emerge which will ultimately benefit the whole mankind. Table 2.1. Candidate refrigerants for replacing CFCs 7 Version 1 ME, IIT Kharagpur
  • 33. Q. Ethyl ether was the first refrigerant to be used commercially, because: a) It exists as liquid at ambient conditions b) It is safe c) It is inexpensive d) All of the above Ans. a) Q. Ammonia is one of the oldest refrigerants, which is still used widely, because: a) It offers excellent performance b) It is a natural refrigerant c) It is inexpensive d) All of the above Ans. d) Q. In the olden days Carbon dioxide was commonly used in marine applications as: a) It has low critical temperature b) Its operating pressures are high c) It is non-toxic and non-flammable d) It is odorless Ans. c) Q. Sulphur dioxide was mainly used in small refrigeration systems, because: a) It is non-toxic and non-flammable b) It has small refrigeration effect c) It is expensive d) It was easily available Ans. b) Q. Need for synthetic refrigerants was felt, as the available natural refrigerants: a) Were not environment friendly b) Suffered from several perceived safety issues c) Were expensive d) Were inefficient Ans. b) Q. The synthetic CFC based refrigerants were developed by: a) Partial replacement of hydrogen atoms in hydrocarbons by chlorine, fluorine etc. b) Modifying natural refrigerants such as carbon dioxide, ammonia c) Modifying inorganic compounds by adding carbon, fluorine and chlorine d) Mixing various hydrocarbons Ans. a) Q. The synthetic refrigerants were extremely popular as they are: a) Environment friendly b) Mostly non-toxic and non-flammable c) Chemically stable d) Inexpensive Ans. b) and c) Q. CFC based refrigerants are being replaced as they are found to: a) Cause ozone layer depletion b) Consume more energy c) React with several materials of construction d) Expensive Ans. a) 8 Version 1 ME, IIT Kharagpur
  • 34. 2.3. Compressor development – a brief history Compressor may be called as a heart of any vapour compression system. The rapid development of refrigeration systems is made possible due to the developments in compressor technologies. 2.3.1. Reciprocating compressors: The earliest compressor used by Jakob Perkins is a hand-operated compressor, very much like a hand operated pump used for pumping water. Harrison also used a hand-operated ether compressor in 1850, but later used steam engine driven compressors in commercial machines. A small half horsepower (hp) compressor was used as early as 1857 to produce 8 kg of ice per hour. Three other machines with 8 to 10 hp were in use in England in 1858. In 1859, the firm P.N. Russel of Australia undertook the manufacture of Harrison’s machines, the first compressors to be made with two vertical cylinders. The firm of Siebe brothers of England went on perfecting the design of the early compressors. Their first compressors were vertical and the later were horizontal. From 1863 to 1870, Ferdinand Carre of France took out several patents on diaphragm compressors, valves etc. Charles Tellier used a horizontal single cylinder methyl ether compressor in 1863. These compressors were initially installed in a chocolate factory near Paris and in a brewery in USA in 1868. In 1876 the ship “Le Frigorifique” was equipped with three of Tellier’s methyl ether compressors and successfully transported chilled meat from Rouen in France to Buenos Ayres in Argentina (a distance of 12000 km). T.S.C. Lowe (1832-1913) started making carbon dioxide compressors in 1865, and began to use them in the manufacture of ice from 1868. However, the credit for perfecting the design of carbon dioxide compressor goes to Franz Windhausen of Germany in 1886. The British firm J&E Hall began the commercial production of carbon dioxide compressors in 1887. They started manufacturing two-stage carbon dioxide compressors since 1889. Soon the carbon dioxide systems replaced air cycle refrigeration systems in ships. Several firms started manufacturing these compressors on a large scale. This trend continued upto the Second World War. A significant development took place in 1876 by the introduction of a twin cylinder vertical compressor working with ammonia by Carl von Linde. Similar to his earlier methyl ether compressor (1875) a bath of liquid mercury was used to make the compressor gas-tight. This ammonia compressor was installed in a brewery in 1877 and worked there till 1908. In 1877, Linde improved the compressor design by introducing a horizontal, double acting cylinder with a stuffing box made from two packings separated by glycerine (glycerine was later replaced by mineral oil). Figure 2.1 shows the schematic of Linde’s horizontal, double acting compressor. This design became very successful, and was a subject of many patents. Several manufacturers in other countries adopted this design and manufactured several of these compressors. USA began the production of ammonia compressors on a large scale from 1880. Raoul Pictet invented the sulphur dioxide compressor in 1874. The machine was initially built in Geneva, then in Paris and afterwards in some other countries. The compressor developed by Pictet was horizontal and was not lubricated as sulphur dioxide acts 9 Version 1 ME, IIT Kharagpur
  • 35. Fig.2.1. Schematic of Linde’s horizontal, double acting compressor as an auto-lubricant. As mentioned before, the sulphur dioxide system was an instant success and was used for almost sixty years, especially in small systems. In 1878, methyl chloride system was introduced by Vincent in France. The French company Crespin & Marteau started manufacturing methyl chloride compressors from 1884. This continued upto the first world war. Escher Wyss of USA started making these compressors from 1913 onwards, right upto the Second World War. At the beginning of 20th century, practically all the compressors in USA, Great Britain and Germany used either ammonia or carbon dioxide. In France, in addition to these two, sulphur dioxide and methyl chloride were also used. Compressor capacity comparison tests have been conducted on different types of compressors as early as 1887 in Munich, Germany. Stetefeld in 1904 concluded that there was no marked difference in the performance of ammonia, carbon dioxide and sulphur dioxide compressors. Due to many similarities, the early compressors resembled steam engines in many ways. Like early steam engines, they were double acting (compression takes place on both sides of the piston). Both vertical and horizontal arrangements were used, the former being popular in Europe while the later was popular in USA. A stuffing box arrangement with oil in the gap was used to reduce refrigerant leakage. The crosshead, connecting rod, crank and flywheel were in the open. Initially poppet valves were used, which were later changed to ring-plate type. The cylinder diameters were very large by the present day standards, typically around 500 mm with stroke lengths of the order of 1200 mm. The rotational speeds were low (~ 50 rpm), hence the clearances were small, often less than 0.5 % of the swept volume. Due to generous valve areas and low speed the early compressors were able to compress mixture of vapour as well as liquid. Slowly, the speed of compressors have been increased, for example for a 300 kW cooling capacity system, the mean speed was 40 rpm in 1890, 60 in 1900, 80 in 1910, 150 to 160 in 1915, and went upto 220 in 1916. The term “high speed” was introduced in 1915 for compressors with speeds greater than 150 rpm. However, none of the compressors of this period exceeded speeds of 500 rpm. However, compressors of very large capacities (upto 7 MW cooling capacity) were successfully built and operated by this time. In 1905 the American engineer G.T. Voorhees introduced a dual effect compressor, which has a supplementary suction orifice opened during compression so that refrigerant can be taken in at two different pressures. As mentioned, the first two-stage carbon dioxide compressor was made in 1889 by J&E Hall of England. Sulzer Company developed the first two-stage ammonia compressor in 1889. York Company of USA made a two-stage ammonia compressor in 1892. 10 Version 1 ME, IIT Kharagpur
  • 36. About 1890, attention was focused on reducing the clearance space between the piston and cylinder head (clearance space) in order to increase the capacity of the compressors. Attention was also focused on the design of stuffing box and sealing between piston and cylinder to reduce refrigerant leakage. In 1897 the Belgian manufacturer Bruno Lebrun introduced a rotary stuffing box, which was much easier to seal than the reciprocating one. A rotating crankshaft enclosed in a crankcase drove the two opposed horizontal cylinders. Many studies were also conducted on compressor valves as early as 1900. By 1910, the heavy bell valves were replaced by much lighter, flat valves. By about 1900, the design of stuffing box for large compressors was almost perfected. However, for smaller compressors the energy loss due to friction at the stuffing box was quiet high. This fact gave rise to the idea of sealed or hermetic compressor (both compressor and motor are mounted in the same enclosure). However, since the early electric motors with brushes and commutator and primitive insulation delayed the realization of hermetic compressors upto the end of First World War. As mentioned, the earliest compressors were hand operated. Later they were driven by steam engines. However, the steam engines gradually gave way to electric motors. Diesel and petrol engine driven compressors were developed much later. In USA, 90% of the motive power was provided by the steam engine in 1914, 71% in 1919, 43% in 1922 and 32% in 1924. This trend continued and slowly the steam engine driven compressors have become almost obsolete. Between 1914 and 1920, the electric motor was considered to be the first choice for refrigerant compressors. About 1920, high-speed compressors (with speeds greater than 500 rpm) began to appear in the market. The horizontal, double acting compressors were gradually replaced by multi-cylinder, vertical, uni-flow compressors in V- and W- arrangement, the design being adopted from automobile engine design. In 1937, an American compressor (Airtemp) comprised two groups of 7 cylinders arranged radially at both ends of 1750 rpm electric motor. These changes resulted in a reduction of size and weight of compressor, for example, a York 300 000 kcal/h compressor had the following characteristics: Year Refrigerant No. of cylinders Speed (rpm) Cooling capacity per unit weight 1910 NH3 2 cylinders 70 6.5 kcal/h per kg 1940 NH3 4 cylinders 400 42 kcal/h per kg 1975 R22 16 cylinders in 1750 200 kcal/h per kg W-arrangement All the compressors developed in the early stages are of “open” type. In the open type compressors the compressor and motor are mounted separately. The driving shaft of the motor and the crankshaft of the compressor are connected either by a belt drive or a gear drive. With the open type compressors there is always a possibility of refrigerant leakage from an open type compressor, even though the rotating mechanical seals developed reduced the leakage rate considerably. Since leakage cannot be eliminated completely, systems working with open type compressors require periodic servicing and maintenance. Since it is difficult to provide continuous maintenance on small systems (e.g. domestic refrigerators), serious thought was given to tackle this problem. A hermetic or sealed compressor was the outcome of this. 11 Version 1 ME, IIT Kharagpur
  • 37. An Australian Douglas Henry Stokes made the first sealed or hermetic compressor in 1918. Hermetic compressors soon became extremely popular, and the rapid development of small hermetic compressors has paved the way for taking the refrigeration systems to the households. With the capacitor starting of the electric motor becoming common in 1930s, the design of hermetic compressors was perfected. In 1926, General Electric Co. of USA introduced the domestic refrigerator working with a hermetic compressor. Initially 4-pole motors were used. After 1940 the 4-pole motors were replaced by 2-pole motors, which reduced of the compressor unit significantly. Soon the 2-pole hermetic refrigerant compressor became universal. Gradually, the capacity of hermetic compressors was increased. Now-a - days hermetic compressors are available for refrigerating capacities starting from a few Watts to kilowatts. At present, due to higher efficiency and serviceability, the open type compressors are used in medium to large capacity systems, whereas the hermetic compressors are exclusively used in small capacity systems on a mass production. The currently available hermetic compressors are compact and extremely reliable. They are available for a wide variety of refrigerants and applications. Figure 2.2 shows cut view of a hermetic compressor. Fig.2.2. Cut view of a hermetic compressor Other types of compressors: 2.3.2.Positive displacement type (other than reciprocating): In 1919, the French engineer Henri Corblin (1867-1947) patented a diaphragm compressor, in which the alternating movement of a diaphragm produced the suction and compression effects. Initially these compressors were used for liquefying chlorine, but later were used in small to medium capacity systems working with ammonia, carbon dioxide etc. Several types of rotary air compressors existed before the First World War, and this idea has soon been extended to refrigerants. However, they became popular with the introduction of Freons in 1930s. The first positive displacement, rotary vane compressor using methyl chloride was installed on an American ship “Carnegie”. However, a practical 12 Version 1 ME, IIT Kharagpur
  • 38. positive displacement, rotary vane compressor could only be developed in 1920. In Germany, F.Stamp made an ethyl chloride compressor of 1000 kcal/h capacity. In USA, Sunbeam Electric made small sulphur dioxide based rotary sliding vane compressors of 150 kcal/h capacity, rotating at 1750 rpm for domestic refrigerators. In 1922, Sulzer, Switzerland made “Frigorotor” of 1000 to 10000 kcal/h using methyl chloride. Sulzer later extended this design to ammonia for large capacities (“Frigocentrale”). Escher Wyss, also of Switzerland rotary sliding vane compressor “Rotasco” in 1936. These compressors were also made by Lebrun, Belgium in 1924 and also by Grasso (Netherlands). A model of the rolling piston type compressor was made in 1919 in France. This compressor was improved significantly by W.S.F. Rolaff of USA in 1920 and M. Guttner of Germany in 1922. Rolaff’s design was first tried on a sulphur dioxide based domestic refrigerator. Guttner’s compressors were used with ammonia and methyl chloride in large commercial installations. Hermetic, rolling piston type compressors were made in USA by Frigidaire for refrigerant R114, by General Electric for ethyl formate and by Bosch in Germany for sulphur dioxide. In 1931, Vilter of USA made large rotary compressors (200000 kcal/h) first for ammonia and then for R12. At present, positive displacement rotary compressors based on sliding vane and rolling piston types are used in small to medium capacity applications all over the world. These compressors offer the advantages of compactness, efficiency, low noise etc. However, these compressors require very close manufacturing tolerances as compared to reciprocating compressors. Figure 2.3 shows the schematic of a rolling piston compressor. The low pressure refrigerant from the evaporator enters into the compressor from the port on the right hand side, it gets compressed due to the rotation of the rolling piston and leaves the compressor from the discharge valve on the left hand side. Fig.2.3. Schematic of a rolling piston type, rotary compressor The screw compressor is another important type of positive displacement compressor. The screw compressors entered into refrigeration market in 1958, even though the basic idea goes back to 1934, by A. Lysholm of Sweden. The screw compressors are of twin-screw 13 Version 1 ME, IIT Kharagpur
  • 39. (two helical rotors) type or a single-screw (single rotor) type. The twin-screw compressor uses a pair of intermeshing rotors instead of a piston to produce compression. The rotors comprise of helical lobes fixed to a shaft. One rotor is called the male rotor and it will typically have four bulbous lobes. The other rotor is the female rotor and this has valleys machined into it that match the curvature of the male lobes. Typically the female rotor will have six valleys. This means that for one revolution of the male rotor, the female rotor will only turn through 240 deg. For the female rotor to complete one cycle, the male rotor will have to rotate 11/2 times. The single screw type compressor was first made for air in 1967. Grasso, Netherlands introduced single screw refrigerant compressors in 1974. The screw compressor (both single and twin screw) became popular since 1960 and its design has almost been perfected. Presently it is made for medium to large capacity range for ammonia and fluorocarbon based refrigerants. It competes with the reciprocating compressors at the lower capacity range and on the higher capacity side it competes with the centrifugal compressor. Due to the many favorable performance characteristics, screw compressors are taking larger and larger share of refrigerant compressor market. Figure 2.4 shows the photograph of a cut, semi-hermetic, single-screw compressor. Fig.2.4. Cut view of a semi-hermetic, single-screw compressor The scroll compressor is one of the more recent but important types of positive displacement compressors. It uses the compression action provided by two intermeshing scrolls - one fixed and the other orbiting. This orbital movement draws gas into the compression chamber and moves it through successively smaller “pockets” formed by the scroll’s rotation, until it reaches maximum pressure at the center of the chamber. There, it’s released through a discharge port in the fixed scroll. During each orbit, several pockets are compressed simultaneously, so operation is virtually continuous. Figure 2.5 shows gas flow pattern in a scroll compressor and Fig.2.6 shows the photograph of a Copeland scroll compressor. The principle of the scroll compressor was developed during the early 1900's and was patented for the first time in 1905. Although the theory for the scroll compressor indicated a machine potentially capable of reasonably good efficiencies, at that time the technology simply didn't exist to accurately manufacture the scrolls. It was almost 65 years later that the concept was re-invented by a refrigeration industry keen to exploit the potentials 14 Version 1 ME, IIT Kharagpur
  • 40. of scroll technology. Copeland in USA, Hitachi in Japan introduced the scroll type of compressors for refrigerants in 1980s. Scroll compressors have been developed for operating temperatures in the range of 45°C to +5°C suitable for cold storage and air conditioning applications. This scroll has also been successfully applied throughout the world in many freezer applications. Today, scroll compressors are very popular due to the high efficiency, which results from higher compression achieved at a lower rate of leakage. They are available in cooling capacities upto 50 kW. They are quiet in operation and compact. However, the manufacturing of scroll compressors is very complicated due to the extremely close tolerances to be maintained for proper operation of the compressor. Fig.2.6. Photograph of a cut scroll compressor (Copeland) 15 Version 1 ME, IIT Kharagpur Fig.2.5. Gas flow in a scroll compressor
  • 41. 2.3.3. Dynamic type: Centrifugal compressors (also known as turbocompressors) belong to the class of dynamic type of compressors, in which the pressure rise takes place due to the exchange of angular momentum between the rotating blades and the vapour trapped in between the blades. Centrifugal were initially used for compressing air. The development of these compressors is largely due to the efforts of Auguste Rateau of France from 1890. In 1899, Rateau developed single impeller (rotor) and later multi-impeller fans. Efforts have been made to use similar compressors for refrigeration. In 1910, two Germans H. Lorenz and E. Elgenfeld proposed the use of centrifugal compressors for refrigeration at the International Congress of Refrigeration, Vienna. However, it was Willis H. Carrier, who has really laid the foundation of centrifugal compressors for air conditioning applications in 1911. The motivation for developing centrifugal compressors originated from the fact that the reciprocating compressors were slow and bulky, especially for large capacity systems. Carrier wanted to develop a more compact system working with non-flammable, non-toxic and odorless refrigerant. In 1919, he tried a centrifugal compressor with dichloroethylene (C2H2Cl2) and then dichloromethane (CCl2H2). In 1926 he used methyl chloride, and in 1927 he had nearly 50 compressors working with dichloroethylene. The centrifugal compressors really took-off with the introduction of Freons in 1930s. Refrigerant R11 was the refrigerant chosen by Carrier for his centrifugal compressor based air conditioning systems in 1933. Later his company developed centrifugal compressors working with R12, propane and other refrigerants for use in low temperature applications. In Switzerland, Brown Boveri Co. developed ammonia based centrifugal compressors as early as 1926. Later they also developed large centrifugal compressors working with Freons. Till 1950, the centrifugal compressors were used mainly in USA for air conditioning applications. However, subsequently centrifugal compressors have become industry standard for large refrigeration and air conditioning applications all over the world. Centrifugal compressors developed before 1940, had 5 to 6 stages, while they had 2 to 3 stages between 1940 to 1960. After 1960, centrifugal compressors with a single stage were also developed. Subsequently, compact, hermetic centrifugal compressor developed for medium to large capacity applications. The large diameter, 3600 rpm machines were replaced by compact 10000 to 12000 rpm compressors. Large centrifugal compressors of cooling capacities in the range of 200000 kcal/h to 2500000 kcal/h were used in places such as World Trade Centre, New York. Figure 2.7 shows cut-view of a two-stage, semi-hermetic centrifugal compressor. Fig. 2.7 Cut-view of a two-stage, semi-hermetic centrifugal compressor. 16 Version 1 ME, IIT Kharagpur